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THE ELEMENTS 


ELECTRIC LIGHTING, 

INCLUDING 


ELECTRIC GENERATION, MEASUREMENT, STORAGE, 

AND DISTRIBUTION. 


BY 

PHILIP ATKINSON, A.M., Ph.D., 

AUTHOR OF “ ELEMENTS OF STATIC ELECTRICITY,” “ THE ELEMENTS OF DYNAMIC 
ELECTRICITY AND MAGNETISM,” “ THE ELECTRIC TRANSFORM¬ 
ATION OF POWER,” “ELECTRICITY FOR EVERYBODY.” 



NINTH EDITION , FULLY RE VISED . 
AND NE IV MA TIER 


NEW YORK: 



D. VAN NOSTRAND COMPANY, 

23 Murray and 27 Warren Street. q >)M c ( ' 

97 TWO COPIES RECEIVED 







Copyright, 1888 , 

By PHILIP ATKINSON. 


Copyright, 1897 , 
BY PHILIP ATKINSON. 

All rights reserved. 


ROBERT DRUMMOND, KDKCTROTYJ’FR AND PRINTER, NEW YORK. 





INTRODUCTION. 


The object of this volume is to meet the demand for 
a, complete, comprehensive treatise, setting forth the 
various facts pertaining to electric lighting in plain 
language, devoid of technicality and perplexing mathe¬ 
matical formulae, from which business men, mechanics, 
and those who have the care and management of dyna¬ 
mos and lamps, as well as general readers, may gain a 
knowledge of the principles and construction of the 
apparatus by which this light is produced, and of the 
nature of that invisible, intangible agency which is its 
prime cause. It is also designed as a convenient hand¬ 
book for the electrical engineer, from which he may 
refresh his memory in regard to the apparatus described 
and its use, or gain a hint as to the nature of electricity 
as developed in its practical application. 

As the storage battery has become an important 
auxiliary in electric lighting, a full description of its 
construction, principles, and application has been given, 
and also of the inductive, alternating current system, 
which has recently been so largely developed. 

Among other sources of information, the writer has 

• • • 
w 



tv 


INTRODUCTION. 


freely consulted the excellent works of Thompson, 
Schellen, Maier, Gordon, Niaudet, and Gladstone and 
Tribe, and has availed himself of the advantage of 
various cuts used by them, illustrating principles and 
apparatus. He also takes great pleasure in acknowl¬ 
edging his obligations to the various electric light com¬ 
panies whose apparatus is described, for highly valuable 
practical information and the free use of numerous 
cuts; also to the various electric journals for similar 
information, especially to the “Electrical Engineer,” 
“Electrical World,” and “Western Electrician.” 


Chicago, Aug. 16, 1888. 


PHILIP ATKINSON. 


Introductory Note to the Ninth Edition. 


Important changes made in the constrnction of dyna¬ 
mos within the last five years have rendered a complete 
and thorough revision of chapters III and IY necessary; 
since most of the dynamos described in the first edition 
have gone out of nse, and new dynamos, chiefly of the 
multipolar type, and designed for heavier work, have 
taken their place. The latter are here described in full, 
instead of the former. 

It has also been found desirable to reverse the relative 
positions of these two chapters, placing the one on 
“Direct Current Dynamos” directly after chapter II, 
in which the principles of the dynamo are illustrated by 
dynamos of this type. 

Two new kinds of storage batteries have been de¬ 
scribed, instead of two which have gone out of use. A 
brief description of vacuum tube lighting has also been 
introduced, and important additions made to the descrip¬ 
tion of arc lamps, transformers, and electric units; and 
thirty-one new illustrations take the place of the same 
number of old ones. 

These changes and additions comprehend all that are 
strictly required to bring the information furnished in 
this book fully up to date. 

PHILIP ATKINSON. 

Chicago, Oct. 1, 1897, 




CONTENTS 


CHAPTER I. 

Electricity a Mode of Molecular Motion 


PAGE 

1 


CHAPTER II. 

Principles of the Dynamo.14 

The Dynamo. — The Armature. — The Commutator. — Closed Circuit and 
Open Circuit Armatures.—The Brushes. — The Field Magnets. — The 
Dynamo’s Mode of Action.—Difference of Potential. — Reversed Cur¬ 
rents. — Commutation. — The Armature’s Mode of Action. — Series, 

Shunt, and Compound Winding. — Constant Current Dynamo. — Constant 
Potential Dynamo.—Direct Current and Alternating Current Dynamos. 

CHAPTER III. 

Direct Current Dynamos.40 

The Excelsior Dynamo. — The Brush Dynamo. — The Thomson-IIouston 
Dynamo.—The Wood Dynamo.— The General Electric Co.’s Multipolar 
Dynamos.—The Siemens-Halslte Dynamo, Type I. 

CHAPTER IV. 

Alternating Current Dynamos.85 

Principles of the Alternating Current Dynamo.—The Wood Single-Phase, 
Constant Potential Alternator. — The Stanley Two-Phase Alternator. — 

The Westinghouse Two-Phase, Constant Potential Alternator. — The 
Converter.—The Westinghouse Rotary Transformer.—Relative Importance 
of Alternating Current Dynamos. 


CHAPTER V. 

Electric Terms and Units. 127 

Electric Potential. — Electro motive Force. — Resistance. — Current. — 
Electric Induction. — Magnetic Induction. —Conductivity and Insulati 
— Quantity and Intensity. — Electric Units. — The Volt. — The Ohm.-— 

The Ampere. — The Ampere-Hour. — The Coulomb. —The Farad. —The 
Microfarad.—The Watt.—The Electric Horse-Power, - The Joule.-The 
Henry. 



VI 


CONTENTS. 


CHAPTER VI. 

PAGE 

Electric Measurement . . . . .... 145 

The Potential Indicator.— Voltmeters and Ammeters.—The Weston 

Voltmeter — The Weston Ammeter. — The Weston Milliammeter. — 

The Wirt Voltmeter. — Ayrton & Perry’s Spring Voltmeters and Am¬ 
meters.—Gravity Ammeters.—The Cardew Voltmeter.—The Edison 
Current Meter.—The Forbes Coulomb Meter.—The Thomson Record¬ 
ing Watt-Meter—Measurement of Electric Resistance.—Resistance 
Coils.—The Standard Light-Unit.—The Bunsen Photometer. 

CHAPTER VII. 

The Arc Lamp.1T6 

Principles of the Arc Lamp. — Arc-Light Carbons. — The Jablochkoff 
Electric Candle. — The Jamin Electric Candle. — The Sun Lamp. — Auto¬ 
matic Adjustment of Arc-Light Carbons. — The Foucault-Duboscq Lamp. 

—The Serrin-Lontin Lamp.—The Brush Arc-Light Lamp.—The Inclosed 
Arc Lamp. 

CHAPTER VIII. 

The Incandescent Lamp.200 

Reynier’s Lamp. — Early Experiments. — Incandescent-Light Carbons. — 

The Edison Carbons. — The Lane-Fox Carbons. — The Cruto Carbons. — 

The Swan Carbons. — The Weston Carbons.—The Bernstein Carbons. 

— General Details of Filament Construction. — Construction of the Incan¬ 
descent Lamp. — Positiou of Lamp. —Vacuum Tube Lighting. 

CHAPTER IX. 

The Storage Battery.229 

Electric Storage. — Plante’s Secondary Cell. — Chemical Reaction In the 
Plante Cell. — The Plante Battery. — Fame’s Secondary Cell. — Chemical 
Reaction in the Faure Cell. — Faults of the Faure Cell. — The Improved 
Faure Secondary Cell. — Electric Formation of the Plates. — Electro- 
Motive Force, Resistance and Current of Cell. — Cause of Buckling. 

—Variable Resistance of Electrolyte.—The American Cell.—The Chloride 
Accumulator.— Durability of Storage Cells. 

CHAPTER X. 

Electric Distribution.249 

Arc-Light Distribution. — Series Installation. — Ilefner von Alteneck’s 
Regulator.— Incandescent-Light Distribution. — The Direct Current Sys¬ 
tem.— Parallel Installation. — Multiple Series Installation. — Series Multi¬ 
ple Installation. —Combined Arc and Incandescent Installation.—The 
Edison Three-Wire System.— The Storage Battery System. — The Induced 
Alternating Current System.— The Primary Alternating Current System. 

— Meters. — Fuses. — Switch-Boards. — Lighting Mines. — Installation 
Rules. 


THE ELEMENTS 

OF 

ELECTRIC LIGHTING. 


CHAPTER I. 

Electricity a Mode of Molecular Motion. 

Introductory Note. — To understand clearly what 
electricity is capable of doing, it is important to ascer¬ 
tain, if possible, wnat it is ; and wnne it can not perhaps 
be shown with absolute certainty that the long-sought 
solution of this problem has been found, yet the proofs 
from numerous sources converge chiefly in the direction 
indicated in this chapter; and in all the various phe¬ 
nomena pertaining to electric lighting, the theory here 
set forth is found to be closely in accordance with the 
facts; hence it has been deemed important to make it 
the introduction to the phenomena to be described 
hereafter. 


The elementary components of the natural universe 
are matter and energy. Matter in the abstract is inert, 
it can move or act only as actuated b^ energy, and 
energy in the abstract is incapable of movement or 
action except through the medium of matter. But we 

1 




THE ELEMENTS OF ELECTRIC LIGHTING. 


2 

have no actual knowledge of either in the abstract, nor 
can we separate them, and all our conceptions of them 
in this respect are theoretical. All matter, even when 
apparently inert, is under the influence of energy, both 
in respect to its mass and its molecules. The apparent 
inertness of the mass is only relative. A steel rail, 
resting in its place on the track, is relatively inert with 
respect to its immediate surroundings, but as a part of 
the earth it partakes of the earth’s motion as a mass; 
and close observation and measurement show that its 
dimensions are subject to continual variation with con¬ 
tinual change of temperature — the result of expansion 
and contraction, — which proves that its molecules are 
in continual motion. The same is true of the column 
of mercury or alcohol in the thermometer, in which 
change of dimension is more apparent. 

All matter is subject to change of dimension with 
change of temperature, but not all in the same degree. 
In many kinds, as baked wood, bone and ivory, it is 
almost imperceptible, requiring delicate instruments to 
detect it; while in others, as gas, vapor, and mercury, 
it is more prominent; so that if change of dimension 
be accepted as proof of molecular motion, it must be 
admitted that such motion is a constant, natural con¬ 
dition of all matter, since an absolute^ stationary 
temperature may be regarded as a practical impossi¬ 
bility. Hence, the absolute immobility of matter, either 
in its mass or its molecules, must be regarded as a purely 
mental conception, having no existence as an actual fact. 

But even if the maintenance of an absolutely station¬ 
ary temperature could be demonstrated as a possibility, 
such demonstration would not disprove the continuous 
Molecular motion of matter, since it has been fully 


ELECTRICITY A MODE OF MOLECULAR MOTION. 3 

demonstrated that heat itself is a mode of motion; so 
that to admit the constancy of heat in matter is to 
admit the constancy of molecular motion. 

It is not important to adduce the proofs on which 
this' theory rests. It is sufficient to state that it is 
maintained by. the highest scientific authority, and 
accepted as a fundamental doctrine of modern science. 

Common observation shows that nothing is so hot 
that it can not become hotter, or so cold that it can not 
become colder, heat and cold being merely convenient 
relative terms to express different degrees of tempera¬ 
ture. Steam generated under a pressure of several 
atmospheres is much hotter than when generated under 
* a pressure of one atmosphere. Cold iron is relatively 
warm as compared with colder iron. Even ice itself 
possesses a certain degree of heat. 

The theory of sound, as an undulatory movement of 
the air, is too well established to require the presenta¬ 
tion of proof; and the theory of light, as another form 
of undulatory movement, has also been accepted as a 
well-established doctrine. But in regard to the nature 
of electricity scientific opinion has been greatly divided, 
and no theory yet proposed has been so free from objec¬ 
tion as to be generally accepted. But electric develop¬ 
ment during the last ten years has done much toward 
the settlement of this question; and the theories and 
opinions of the great electricians of the period imme¬ 
diately previous are yielding to the steady pressure of 
recent investigation, just as their investigations modified 
or displaced former theories and opinions. 

Observation shows that electricity may be developed 
in every kind of matter ; from which we may reasonably 
infer that it is a universal property of matter in the 


4 


THE ELEMENTS OF ELECTRIC LIGHTING. 


same sense as heat. In proof of this, we find that it 
may be promptly developed in the numerous class of 
bodies known as non-conductors by means of friction, 
and in the class known as conductors, which embraces 
all other bodies, by the same means, it they are first 
properly insulated. As an example of the latter class, 
we may select a brass rod; let it be insulated and sub¬ 
jected to friction from another insulated body, and elec¬ 
tricity is rapidly developed, as shown by attraction, and 
by the spark and snap. That this electricity is devel¬ 
oped in the rod itself, and not derived from the body 
by which the friction is produced, is proved by using a 
metal friction-brush, or metal in any form bj^ which 
a light contact is obtained. The Varley and Topler 
electric machines are examples of this. In the Arm¬ 
strong hydro-electric machine we have a very notable 
instance of electricity generated by the friction of con¬ 
densed steam, emitted through metal pipes tipped with 
wood. From these, and numerous other instances which 
might be adduced, we may conclude that electricity can 
be developed in all bodies by friction , its development 
in conductors, when insulated, being equally as prac¬ 
ticable as in non-conductors. 

The generation of heat by friction is coincident with 
that of electricity, and the heat continues to increase 
long after the electric development has attained its 
maximum. If the friction be sufficiently increased in 
the case of a solid body, as a metal, light is developed, 
the metal becoming incandescent. Thus, by the agency 
of friction, certain phenomena are produced, the first of 
which we call electricity, the second heat, and the third 
light. The last two we designate as modes of motion. 
Why not the first also? The friction is a result of 


ELECTRICITY A MODE OF MOLECULAR MOTION. 


5 


mechanical energy acting through matter; the energy 
in this form disappears, and is reproduced as electricity, 
heat, and light. Each of these then is a different 
manifestation of energy acting through matter as its 
medium. 

Since these manifestations are different, it is evident 
that each must have its own peculiar form of molecular 
motion; that the electric movement, which becomes 
prominent first, is the most easily and rapidly devel¬ 
oped, and essentially different from the heat movement, 
which, though coincident with it, is developed more 
slowly; while light is not produced till the movement 
has assumed great intensity, the light changing from 
red to white as the intensity increases. 

In the battery we have electricity produced by chem¬ 
ical reaction, and heat also as a coincident result. The 
chemical reaction is itself a mode of atomic and molec¬ 
ular motion by which atoms and molecules interchange 
and form new combinations; and since the incidental 
heat is admitted to be a mode of motion, we may reason¬ 
ably infer that the more prominent electricity is another 
mode of motion ; the energy disappearing in the chem¬ 
ical mode, reappearing in the heat and electric modes 
— molecular motion in one form being transmuted into 
molecular motion in the other two forms. 

In the dynamo we have electricity generated by 
mechanical action combined with magnetic, electricity 
and magnetism reciprocally producing each other. 
Magnetism is admitted to be the result of a certain 
molecular arrangement in the substance of the magnet; 
and in the soft iron of the electro-magnets of the 
dynamo this molecular arrangement undergoes constant 
disturbance, producing a series of momentary electric 


6 THE ELEMENTS OF ELECTRIC LIGHTING. 

currents with such rapidity as to maintain an apparently 
constant electric action. Hence we must infer that 
these magnets are in a constant state of intense molec¬ 
ular motion; and since magnetism and electricity are 
always coexistent and reciprocal, we are warranted in 
the conclusion that they are of the same nature, — sui 
generis ,—and that if one is a mode of molecular motion 
the other must be. And this theory gains additional 
strength from the fact that here again we find heat 
generated as an incidental result, to such an extent 
that special arrangements are required to keep the 
dynamo from being injured by overheating. 

In the thermopile we have electricity, generated by 
the direct agency of heat; and in order to create a dif¬ 
ference of electric potential, which is the principle upon 
which every electric generator is based, a difference of 
heat potential must be created. This is accomplished 
by the use of two metals, usually bismuth and anti¬ 
mony, having different conductivities for heat and 
electricity. Bars of each are smelted together at the 
ends, and arranged in compact form in an alternating 
series, in such a manner that one set of junctions can 
be heated while the alternate opposite set is cooled. 
The electric current flows across each heated junction 
from bismuth to antimony, and across each cooled 
junction from antimony to bismuth, so that at each 
junction it receives a fresh impulse in the same gen¬ 
eral direction, since the heated and cooled junctions 
alternate. The specific capacity of bismuth for heat 
is 0.030, and that of antimony, 0.051, that of water 
being unity ; and the temperature of each, when heated 
or cooled from the same source, varies inversely as 
this specific capacity; hence, at the heated junctions 


electricity a mode of molecular motion. 


the temperature of the bismuth rises above that of the 
antimony, and at the cooled junctions falls below it; 
and as the heat movement as well as the electric move¬ 
ment is from higher to lower potential, we find here an 
exact correspondence in the movement of each. 

But there is also a difference in the molecular consti¬ 
tution of the two metals, as indicated by their crystalline 
structure, bismuth crystallizing in one form while anti¬ 
mony crystallizes in another; and the greater the dif¬ 
ference in this respect, as well as in conductivity for 
heat and electricity, between these or any other two 
metals, the more energetic the thermoelectric action. In¬ 
deed this difference in crystalline structure, and hence in 
molecular constitution, is undoubtedly the cause of the 
difference in conductivity; the difference in electric 
and heat potentials corresponding, as shown, to the 
difference in electric and heat conductivities. 

But we have also in this instrument an instance of 
the reciprocal action between heat and electricity. If 
instead of heating and cooling alternate junctions to 
generate electricity, an electric current is passed through 
from an external source, the junctions become heated 
or cooled according to the direction of the current. A 
current passed through a bismuth-antimony pair from 
antimony to bismuth heats the junction, while if passed 
through from bismuth to antimony the junction is cooled. 
According to the doctrine that heat is a mode of motion, 
the heating is an increase in the intensity of motion, 
and the cooling a decrease of that intensity; and in 
this experiment the reduction of temperature has been 
carried to such an extent that water has been frozen in 
cavities made in the metals. It will also be perceived 
that the same correspondence of movement between 


8 


THE ELEMENTS OF ELECTRIC LIGHTING . 


heat and electricity exists in the reciprocal action by 
which heat is generated, as in the direct action by 
which electricity is generated. 

The generation of electricity by light, or, as Dr. 
Werner Siemens terms it, “the direct conversion of 
the energy of light into electric energy,” has received the 
attention of leading electricians, and led to the inven¬ 
tion of instruments for that purpose ; and, although the 
invention is still confined to the laboratory, enough is 
known to demonstrate the possibility of such conver¬ 
sion, and hence to establish the fact of such an intimate 
relation between these two different manifestations of 
energy as to indicate the probability of a similar nature. 
The means employed is, in some respects, not unlike 
that already described for the generation of electricity 
by heat, — a combination ot metals differing in molecu¬ 
lar construction and conductivitv. But in this case 
metal plates are used; and selenium seems to have the 
preference, combined with gold and some base metal. 

The accepted doctrine of light as a mode of motion 
is too well known to require elucidation here; but the 
nature of the instrument above referred to, and the re 
quirement of metals for its construction differing in 
molecular constitution, indicate that the mode of mo¬ 
tion known as light is changed by contact with the 
metals into the mode of motion known as electricity, 
either by this contact generating the resulting mode of 
motion in the metals themselves, or in some medium 
permeating their structure. 

The action then in all these modes of generation is 
both direct and reciprocal. Heat produces electricity, 
and electricity produces heat; magnetism produces elec¬ 
tricity, and electricity magnetism ; light produces elec- 


ELECTRICITY a mode of molecular motion. 


0 


tricity, and electricity light. There is also reciprocal 
action between mechanical motion and electricity; but 
the connection is not so close and intimate as between 
the different forms of molecular motion, in which proof 
in regard to the nature of one becomes proof in regard 
to the nature of the other. 

Thus far we have confined our attention to electric 
generation, but electric transmission is of equal impor¬ 
tance in elucidating our subject; for if we could satis¬ 
factorily determine how electricity is transmitted, we 
should be in a fair way to determine what it is. 

Assuming the truth of our original proposition, that 
energy is inseparable from matter, and that electricity 
is one of the forms in which energy manifests itself, a 
medium, consisting of matter in some form, is essential 
to its transmission. On this point there are two theo¬ 
ries; one, that energy uses the different forms of tan¬ 
gible matter as its medium ; the other, that all tangible 
matter — solid, liquid, and gaseous—is permeated by a 
certain intangible fluid known as ether, which consti¬ 
tutes the medium for electric transmission. The for¬ 
mer theory assumes that electric transmission is by 
vibrations of the tangible matter itself, the latter, that 
it is by vibrations of the intangible ether. As both 
theories assume a mode of motion, and are in this 
respect equally well adapted to our purpose, it is unne¬ 
cessary to enter into the discussion of their respective 
merits, further than to say, that the existence of ether 
has never been demonstrated, that the ether theory is 
unsupported except by inferential proof, and that the 
transmission of electric energy by the vibratory motion 
of tangible matter is the more reasonable theory of the 
two, and far more susceptible of demonstration. 


10 


THE ELEMENTS OF ELECTRIC LIGHT I NO. 


The theory of the universal ether was originally in¬ 
vented to meet the necessity of a medium lor the trans¬ 
mission of light through the interplanetary spaces, 
where it has been supposed that air can not exist, and 
its adaptation to electricity is of more recent origin. 
But the theory of the existence of a universal atmos¬ 
phere, like that of the earth, has strong support, though, 
in the interplanetary spaces, it must be almost as im¬ 
palpable as the supposed ether itself. 

The two important factors in electric transmission 
are conductivity and resistance; one of which is always 
in the inverse ratio of the other, and the relative pro¬ 
portions of each in every substance constitute the dif¬ 
ference between the conductor and the non-conductor. 
We may assume that electric transmission depends 
on molecular structure, that in good conductors this 
structure is such as to facilitate transmission, and in 
inferior conductors to retard it, while the structure of 
non-conductors is such as almost wholly to prevent it; 
and we may suppose, that in a good conductor the 
molecules lie in parallel lines, and that the electric 
energy causes each molecule to impinge on the next 
contiguous one, producing an undulation which runs 
through the conductor for perhaps a thousand miles in 
an instant; but that in the inferior conductor, or the 
non-conductor, the molecular arrangement is more or 
less irregular, requiring a wrenching or twisting of the 
molecules to bring them into position. It is evident, 
that in the latter case far greater energy is required to 
produce the same result, and that this series of wrench- 
ings and twistings must result in the coincident de- 

O o 

velopment of that other mode of motion which we term 
heat. So that while in a good conductor, as a copper 


ELECTRICITY A MODE OF MOLECULAR MOTION. 11 


wire, electric transmission is easily effected, and the 
development of heat very slight, in an inferior con¬ 
ductor, as a platinum wire or a carbon filament, the 
heat development rises to incandescence. These results 
indicate that the transmission of electric energy is by 
molecular motion, as assumed, or rather that this mode 
of motion by which this energy manifests itself is that 
which we term electricity. 

According to the old theory of thunder and light¬ 
ning, the passage of electric fluid through the air pro¬ 
duces the flash, and the thunder is a result of the air 
displacement and collapse. This theory is evidently 
incompatible with the theory of electric energy using 
the air as its medium. According to the latter view, 
there is no passage of electric matter through the air, 
and consequently no displacement except that resulting 
from the incidental development of heat. The electric 
discharge takes place along a narrow line, often three 
to five miles or more in length. The air along this line 
becomes incandescent, and is expanded by the intense 
heat; but the partial vacuum thus created is confined 
to this narrow line, and the collapse is quite insufficient 
to account for the terrific peal of thunder which often 
accompanies the flash. But the intense vibration occur¬ 
ring throughout this long line in an infinitesimal moment 
of time must produce the thunder-peal in strict accord¬ 
ance with the well-known laws of sound. It is possible 
that the succession of vibrations following the discharge, 
and set in motion by it, produces the rumble often 
heard, but the one tremendous vibration is the first 
immediate result of the discharge. 

Comparing the results of thunder and lightning witli 
those of explosions of gunpowder and dynamite, we 


12 


THE ELEMENTS OF ELECTRTC LIGHTING. 


find a very essential difference. In the explosion there 
is a displacement of a great volume of air, not confined 
to a single line, but diffused over a large space ; and 
the results of the sudden expansion and collapse are 
often the breaking of glass and the destruction of 
buildings in the immediate vicinity, the effect of the 
air movement being often felt at a distance too great 
for the sound to be audible. But the electric discharge 
takes place over our dwellings, or between earth and 
cloud in our immediate vicinity, accompanied by the 
terrific thunder-peal, often far exceeding the sound of 
the loudest explosion, and the only perceptible effect is 
a slight tremor such as should follow from the vibratory 
movement assumed in our hypothesis. Hence we con¬ 
clude that the transmission of electric energy in this 
case is by a vibratory motion ; or, as before, that this 
mode of motion, so produced, is electricity. 

All electric action is an exhibition of energy, whether 
it be in the movement of a pith ball, in the flash of 
the electric spark, in the brilliancy of the arc light or the 
softer radiance of the incandescent, in the deposition 
of metal by electrolysis, the click of the telegraph, the 
speech-producing movement in the telephone, the pro¬ 
pelling of cars on a railway, or in the lightning’s flash 
rending the oak. It produces chemical decomposition, 
mechanical motion, light and heat. It inflicts pain, 
destroys life, soothes suffering, heals disease. All these 
varied phenomena are different manifestations of energy. 

Since electricity, then, is a product of energy and a 
producer of energy, it is manifestly closely allied to 
energy. But high electric authority says, “ Whatever 
electricity is, it is not energy.” This is true if we speak 
of energy in the abstract. But in this sense neither is 


ELECTRICITY A MODE OF MOLECULAR MOTION. 13 


heat energy, nor light, gravity, or mechanical motion. 
Energy in the abstract is a mere mental conception 
having no actual existence ; it must act through matter 
as its medium, and in this concrete sense there can be 
no more objection to regarding electricity as one of the 
forms in which energy manifests itself than in regard¬ 
ing heat, light, or sound in that sense; and since every 
manifestation of energy is by means of motion, the 
conclusion seems inevitable that electricity is a mode of 
molecular motion. 


CHAPTER II. 







Principles of the Dynamo. 

The requisites for the production of the electric light 
are an electric generator, an electric lamp, and a con¬ 
ductor connecting the generator and lamp. 

The generator must be capable oi producing continu¬ 
ous, steady electric action of sufficient energy tor the 
required work. It may be either an ordinary battery 
or a dynamo. 

From the beginning of the present century until 
about 1867 the battery was the only known generator 
capable of producing the electric light; the electric 
machine, though capable of powerful effects, being 
incapable of producing a continuous electric current. 
All batteries are not equally well adapted to this pur¬ 
pose : the Daniell, Leclanche, and many others, which 
are adapted to various other kinds of electric work, are 
not suitable for the production of the electric light. The 
Bunsen battery can be used; and if a light ot short 
duration only is required, as in surgical examinations 
or theatrical effects, any good carbon-zinc battery will 
answer the purpose. But for a strong light of several 
hours’ duration, the Grove battery is superior to all 
others, 40 to 50 Grove cells being capable of producing 
such a light for two or three hours. From these facts it 
is easy to see why electric lighting, though known as 
early as 1800, was merely a laboratory experiment until 

14 


PRINCIPLES OF TIIE DYNAMO. 


15 


about 1867; the great expense and labor of renewing 
the fluid in 40 or 50 Grove cells once in two or three 
houis being alone sufficient to render the ordinary use 
of the light obtained in this way impracticable, while 
the noxious fumes from such a battery make its use 
tor this purpose practically prohibitory. 

The Dynamo. — In 1867 the previous inventions of 
several leading electricians culminated in the produc¬ 
tion ol the dynamo; and the problem of general electric 
lighting on an economical basis received a practical 
solution, since electricity could now be generated by 
mechanical power at far less cost and in. far greater 



Fig. 1. 


quantity than was possible or practicable by the chemi¬ 
cal process of the battery. 

Without entering into perplexing details, the essen¬ 
tial parts of the dynamo, and its mode of action, may 
be briefly described. These parts are' the armature, the 
field-magnets, the commutator, and the brushes. 


The Armature. — The armature, in its usual form, 
consists of a number of coils of copper wire, wound on 


an iron ring, which is mounted on an axis and revolved 
between the poles of the field-magnets, as shown in 
Fig. 1. The iron ring or core of the armature may 
consist of a number of iron wire rings, or of flat rings 

























16 


THE ELEMENTS OF ELECTRIC LIGHTING. 


stamped out of thin sheet-iron, and placed vertically 
side by side, or of thin iron hoops laid over each other. 
These should be of the best soft iron, and electrically 
insulated from each other by varnish, asbestos, mica, 
or other suitable insulator. Solid iron cores are objec¬ 
tionable, chiefly on account of becoming heated; and 
the cores here described are greatly improved by having 
an open structure, so far as practicable, for the free 
circulation of air, by which the heating is greatly 
reduced. The insulation and composite structure, 
described above, are also important in giving the 
electric current its proper normal direction, and pre¬ 
venting the formation of the electric eddies, known 
as Foucault currents, which waste the energy and 
generate heat, a fault to which solid cores are espe- 

ciallv liable. 

%/ 

The coils shown in the cuts are reduced to a few 
turns of wire and an open structure, but those in actual 
use consist of a number of layers closely wound like 
thread on a spool. The wire should be as large, and 
the number of turns in each coil as numerous, as practi¬ 
cal convenience will admit; the resistance of the wire 
to the passage of the electric current, and the conse¬ 
quent heating, being reduced with increase of size, while 
the electric energy increases with the number of turns; 
each turn adding its quota to the current generated, 
provided the amount of copper is thereby increased; 
but there is no increase of energy by the mere substitu¬ 
tion of fine wire for the same amount of copper in 
coarse wire. The wire in the coils, and in every part 
of the dynamo and its connections through which an 
electric current flows, must be covered with some 
good insulating material, which will confine the cur- 


PRINCIPLES OF THE DYNAMO . 


17 



rent to the direction in which it is designed to flow, 
and prevent its escape from one turn to another, 
or to any object with which the wire may come in 
contact. 

The Commutator. — Figs. 1 and 2 show that the 
ends of the coils connect with cylindric segments at 


the axis of the armature: these constitute the com- 
mutator, whose use will be fully explained hereafter. 
Its segments are of copper or some other suitable metal, 
as phosphor-bronze, or gun-metal; the requisites being 
that the metal must be a good conductor, and not liable 
to heating or corrosion. They are attached to the axis, 
and insulated from it and from each other, and of the 


Fig. 2. 








18 


THE ELEMENTS OE ELECTRIC LIGHTING. 


same number as the coils; and special provisions are 
required to prevent the spaces between segments from 
becoming clogged with conducting material as copper- 
dust, or carbonized oil, by which the insulation is 
reduced or suspended. 

Closed Circuit and Open Circuit Armatures.— 
In some armatures the coils connect with each other all 
around in a closed circuit, while each one connects also 
with a separate segment of the commutator, as shown 
in Fig. 1. In others they are arranged in pairs on 
opposite sides of the ring, each pair being connected 
with opposite segments of the commutator, and inde¬ 
pendent of all others, as shown in Fig. 2. The first kind 
are known as closed circuit armatures, as in the Gramme 
dynamo; the second kind as open circuit armatures, as 
in the Brush dynamo. 

The Brushes. — The brushes by which the electric 
current is taken up and transferred through conductors 
to the lamp are shown in Fig. 2, in their usual position 
in contact with the commutator. They are made of 
copper, and are of different styles, as shown in Fig. 3, 
which shows the under brushes as viewed from above; 
the style at A consisting of two layers of wires soldered 
together at the upper end ; the one at B, of two broad 
strips divided as shown for a certain distance from the 
lower end ; the one at 0, of several undivided strips of 
different lengths, overlapping each other. Sometimes 
two of these styles, as A and B, or A and C, are com¬ 
bined in the same brush. The main object is to obtain 
the best contact at numerous points, and to prevent the 
waste of energy and irregularity caused by sparking at 
the points of contact. The brushes are held in suitable 
clamps in the position shown in Figs. 1 and 2, their free 


PRINCIPLES OF THE DYNAMO. 19 

ends pointing in the direction in which the armature 
revolves; and a steady pressure is maintained by their 
elasticity. 


A 



The Field-Magnets. — In Fig. 1 we have an ideal 
representation of the field-magnets on each side of the 
armature, with their pole-pieces partly inclosing it. 
They may be permanent steel magnets or electro-mag¬ 
nets. Permanent magnets are suitable only for small 


20 


THE ELEMENTS' OF ELECTRIC LIGHTING. 


hand dynamos, designed for experimental laboratory 
work. For this purpose the permanent magnetism is 
an advantage, since there can be no such increase of 
force as to prevent the operation of the dynamo by 
hand, which might be the case with electro-magnets. 
But the low energy of permanent magnets as com¬ 
pared with electro-magnets, and their liability to par¬ 
tial loss of magnetism with age, render them unsuitable 
for dynamos of the energy required for the electric 
light. 

The term electro-magnet is used to designate any 
magnet having an iron core wound with insulated 
wire, through which wire an electric current may be 
transmitted: the armature itself is such a magnet. 
The core becomes magnetic only while the current 
is flowing through the wire; and its magnetism ceases 
with the cessation of the current, leaving only a 
slight trace known as residual magnetism, which in 
dynamos has an important function, as will be ex¬ 
plained hereafter. 

The ends of every magnet are technically termed 
poles, distinguished respectively as north and south by 
the direction in which a straight bar magnet points 
when freely suspended, and marked N. and S. In the 
dynamo, north and south poles face each other; and 
into the space between them, in which the armature 
revolves, lines of magnetic force radiate, constituting 
what is technically termed the magnetic field ; hence 
the magnets are called field-magnets. They may be 
straight magnets, as shown in Fig. 1, a single north 
pole facing a single south pole ; or horse-shoe magnets, 
two north poles alternately facing two south poles. 
The core should be of the best soft iron, either wrought 


PRINCIPLES OF THE DYNAMO. 


21 


or cast. The pole-pieces, which are considerably wider 
than the core, are curved on the faces, inclosing a 
large portion of the armature and confining all the 
lines of force, and are placed as close to the armature 
as safety of rotation will admit, so as to reduce the 
magnetic resistance to its minimum, as the lines of 

O 

force traverse the field; the resistance of the air being 
immensely greater than that of the iron core of the 
armature. 

Cast-iron is generally used for the pole-pieces, but 
wrought-iron is sometimes preferred ; and a laminated 
structure, composed of numerous thin layers combined, 
is also recommended ; the object being, as in the arma¬ 
ture core, to give the lines of force their proper 
direction. 

Lar°*e wire, well insulated, is as essential for the 
winding of the field - magnets as tor that ol the 
armature, for the reasons already given ; and a greater 
body of wire in the central portion of the magnet 
than near the ends is recommended, as giving a 
more even current, less subject to sudden fluctuation, 
which, in an electric-light dynamo, is a very essential 
point. 

The Dynamo’s Mode of Action. — It has been 
shown that lines of magnetic force from the poles of 
the field-magnets radiate into the space between them, 
known as the magnetic field. The direction of these 
lines is from the pole technically known as the north 
to the one known as the south pole, and theii liumbei 
may be considered infinite throughout the field, though 
more numerous in some parts than in othcis. When a 
coil of wire is rotated in this field, temporary electric 
currents circulate in the wire at right angles to the 


22 THE ELEMENTS OF ELECTRIC LIGHTING. 

magnetic lines which pass through the coil, and the 
electromotive force of this current varies as the number 
of those lines. 

Difference of Potential.— It is absolutely necessary, 
in the generation of these currents, that the magnetic 
intensity should vary, or, as technically termed, that there 
should be a difference of magnetic potential at different 
points; and this difference is produced by the different 
relative positions of the armature coils, as they rotate, 
with reference to the lines ot force. As the object of 
every electric generator is to create and maintain a differ¬ 
ence of electric potential, it is evident that if the arma¬ 



ture rotated in a uniform field with its axis parallel to 
the magnetic lines, so that the number intercepted by its 
coils was always the same, there would be no difference, 
either of magnetic or electric potential, and hence no 
current. The generation of current depends on the 
fact that the coils cut across those lines, continually 
changing position and intercepting a number varying 
from zero to a maximum ; the position of each coil with 
reference to the lines being alternately reversed by the 
rotation of the armature, at each half-revolution, as shown 
by Fig. 4, producing alternate reversal of current. 















































PRINCIPLES OF THE DYNAMO. 


23 


The current always Hows from the point where the 
electric pressure is greatest to the point where it is least; 
that is, technically, from higher to lower potential, just 
as water flows from a higher to a lower level, or steam 
rushes through a pipe from where the pressure is greatest 
to where it is least. 

Reversed Currents. —The direction of the current, as 
stated, is always at right angles to that of the magnetic 
lines ; and when by the rotation of the armature the move¬ 
ment of the coils, as viewed from the pole toward which 
the magnetic force moves, is upward next that pole, the 
current circulates in the coils in the same direction as the 
hands of a watch move, as shown at the upper left hand 
corner of Fig. 4; but when the movement is downward 
next the pole from which it moves, the direction of the 
current is reversed, as shown at the lower right-hand 
corner; the latter direction being known as the positive 
sense, and the former as the negative. 

It is evident, then, that at each revolution of the arma 
ture two distinct electric currents are generated in its 
coils, one during each half-revolution ; that each coil 
passes through two neutral points where the currents 
reverse, and where it intercepts a minimum number of 
the magnetic lines, and also through two points where 
it intercepts a maximum number. The generation of 
current begins at the instant the first neutral point is 
passed, increases as the difference in the number of lines 
intercepted per unit of time increases, diminishes as this 
number decreases, and ceases at the second neutral point. 
Here a new current begins, which passes through the 
same phases of increase and decrease during the second 
half-revolution, and the relative position of the coil being 
reversed the direction of the current is reversed also. 


24 


THE ELEMENTS OF ELECTRIC LIGHTING. 


End) of these currents is transitory, its rise, fall, and 
reversal occupying only an instant, and passing into the 
external circuit through the brushes and commutator, or 
collector, as an undulation; and the continuous current 
of the dynamo is composed of a succession of these 
transitory currents, and is direct, if passed through a 
commutator, but otherwise, alternating, as explained here¬ 
after. 

It is not essential to the generation of an electric 
current that the wire should be in the form of a coil ; a 
straight wire, or one bent into any conceivable shape, and 
forming part of a closed circuit, if moved through a field 
of varying magnetic intensity by rotation, or in any other 
manner, will have electric currents generated in it, 
whether it moves from greater to less, or from less to 
greater intensity. Or such a wire or coil, if moved 
through a perfectly uniform field in such a manner as to 
intercept a varying number of lines of force, per unit of 
time, will have electric currents generated in it. It is 
evident, however, that a perfectly uniform field between 
opposite north and south poles is a practical impossibil¬ 
ity, magnetic intensity, north or south, decreasing from 
one pole to the other, each kind in the inverse ratio of 
increase in the opposite kind. The chief advantage of 
the coil consists in its capability of inclosing an iron core, 
which by its magnetic conductivity intercepts and leads 
the lines of force through it, in close proximity to the 
inclosing wire, so as to produce the highest inductive 
effect. 

According to a theory now somewhat obsolete, the 
currents are generated by the lines of force threading 
through the coils, the interior wire thus taking part in 
the generation equally with the exterior ; but experiment 


PRINCIPLES OF THE DYNAMO 


25 


seems to prove that this theory is fallacious, as no current 
is found in the interior and end wire when not continu¬ 
ous with the exterior; its office being apparently that of 
a conductor of the currents generated in the exterior 

wire. 



Commutation.— By reference to Fig. 5, it will be seer* 
that the currents generated in the armature are taken up 
by the brushes and circulate in the direction shown by 
the arrows through the coils of the field-magnets and the 
external circuit in which the lamp is placed. If there 
were no commutator, the currents in this circuit would 












































































































































26 


THE ELEMENTS OF ELECTRIC LIGHTING. 


be alternately reversed, and we would have the alternat¬ 
ing-current dynamo, which constitutes a distinct class; 
but it will be seen by Fig. 6 that at the instant the arma¬ 
ture current is reversed, the position of the opposite seg¬ 
ments of the commutator with reference to the brushes 
is reversed also, each segment as it moves out of contact 



with one brush moving into contact with the opposite 
brush, so that each transitory current, generated in the 
connected coil, passes into the external circuit in the 
same direction by this commutation; for, as shown in 
Fig. 4, the current isalwavs in the same direction in each 
of the two opposite positions of the coils, hence if taken 
up by each brush before reversal, all the currents must 


























PRINCIPLES OF THE DYNAMO. 27 

pass out of the armature at one brush and into it at the 
other, as shown in Fig. 5, and therefore flow in the same 
direction through the external circuit. 

But if there were only two segments and two coils, it 
is evident that a break in the current would occur at each 
half-revolution. But with four segments and four coils 
at right angles to each other, as shown in Fig. 7, and the 



brushes so constructed as to make contact with the ap¬ 
proaching segment before breaking contact with the 
receding segment so as to bridge the intervening space, 
the current becomes continuous, one pair of coils generat¬ 
ing current while the other pair is passing the neutral 
points. But the current though continuous, would be 
uneven, rising and falling in waves as the coils passed 
from the neutral to the maximum points, and round 













28 THE ELEMENTS OF ELECTRIC LIGHTING. 

again to the neutral. This is corrected by multiplying 
the coils and segments, as shown in Fig. 1 (page 15), 
thus multiplying the number of waves and reducing 
their length and intensity in the same ratio. 

In closed circuit armatures, as shown in Fig. 1, all the 
transitory currents on the same side reinforce each other, 
the coils being all connected together, and each con¬ 
nected also with a separate segment of the commutator, 
so that each coil has constant connection with the brushes, 
through the commutator, during the entire revolution of 
the armature. Hence if the brushes were placed at the 
maximum points it is evident that the opposite coils on 
each side would be carried past the neutral points by rota¬ 
tion before the connected commutator segments reached 
the brushes, and the generated currents be neutralized by 
the generation of reversed currents of equal strength, 
and the external current cease. But when the brushes 
are placed at the neutral points, all the currents gener¬ 
ated on the left, when the rotation is in the direction of 
watch hands, as in Fig. 5, pass into the external circuit 
by the upper brush, while those generated on the right 
are augmented by the current flowing in from this 
circuit by the lower brush. Hence since no external 
current is obtained with the brushes at the maximum 
points, while a maximum current is obtained when 
they are at the neutral points, it is evident that, in 
any intermediate position, there must occur a partial 
neutralization by opposing currents ; the neutralization 
decreasing and hence the electromotive force increas¬ 
ing as the brushes approach the neutral points, and these 
conditions being reversed as the brushes approach the 
maximum points. 

By attaching the brushes to an insulating yoke by 


PRINCIPLES OF THE DYNAMO. 


20 


which they can be moved simultaneously to any two 
opposite points, the electromotive force and resulting 
current can thus be regulated as required, within certain 
limits. But such regulation tends to increase sparking 
at the brushes, a wasteful and injurious heating effect, 
difficult to suppress. Dynamos with open-circuit arma¬ 
tures are susceptible of similar regulation. 



Fig. 8. 


The Armature’s Mode of Action. —If the armature 
were constructed without a core, or with one of high 
resistance, its energy would be comparatively low, de¬ 
pending solely on the electricity induced in its coils by the 
field-magnets. The principal advantage of the iron core 
consists, not only in furnishing a medium of high 
magnetic conductivity by which the lines of force are led 
into close proximity with the coils without loss, but 













30 THE ELEMENTS OF ELEOTHIG LIGHTING. 

chiefly because it makes the armature itself an electro- 
magnet, acting reciprocally with the field-magnets to 
multiply the magnetic and electric effects by mutual re¬ 
action. In an armature without an iron core the lines of 
force would run nearly parallel from pole to pole; the 
concavity of the pole-pieces producing parallelism in 
lines which would be divergent if radiated from 
one plane surface to another. The same parallelism is 
found to exist when the magnets are separately excited, 
and the armature is not rotating, as shown in Fig. 8, 
where the lines passing into the armature in the central 


Fig. 9. 



region are seen to be parallel, while those at the extremi¬ 
ties of the pole-pieces, above and below, are slightly 
curved. It will be noticed that the lines are denser near 
the extremities of the pole-pieces than in the center, and 





















PRINCIPLES OF THE DYNAMO. 


31 


that the relative number passing through the interior of 
the armature is comparatively small. 

The field-magnets induce opposite polarity in those por¬ 
tions of the armature core adjacent to each pole, as shown 
in Fig. 9, while the electric currents circulating in the 
armature coils induce in the same parts of the core, 
polarity similar to that of each field-magnet pole, north 
polarity on the right and south polarity on the left, when 
the rotation is in the direction indicated by the arrow. 
This polarity is much stronger than that induced by the 
field-magnets, and on account of the mutual repulsion 
between these poles and the similar poles of the field- 
magnets they are deflected into a position nearly at right 
angles to that of a line joining the field-magnet poles, as 
shown in Fig. 9, the north pole upward to nn , and the 
south downward to s s, the field-magnet poles being, for 
the same reason, deflected into the positions indicated in 
each by the letters n and s. Hence the lines of force 
become greatly contorted, as shown. 

But the armature core does not become fully magnet¬ 
ized at the instant induction occurs, nor fully demagnet¬ 
ized at the instant it ceases, an infinitesimal moment 
being required for magnetic saturation in the first in¬ 
stance and demagnetization in the second, known as mag¬ 
netic lag , during which its poles are moved slightly for¬ 
ward by the rotation, increasing the contortion of the 
lines. 

These positions of the armature’s poles become com¬ 
paratively stationary, varying slightly with the speed of 
rotation, the core rotating through them, and the mag¬ 
netic strength and polarity of each portion changing with 
its position. Hence the neutral line, where the currents 
reverse, is through the armature’s principal poles, nn 


32 


THE 


ELEMENTS OF ELECTRIC LIGHTING 


and s s, its position being diagonal to fliafc of a line 
through the centres of the pole-pieces. 

When a new dynamo is completed and ready for use, 
it is found that the iron, during the various manipula¬ 
tions to which it has been subjected, has become slightly 
magnetic; and this residual magnetism, as it is termed, 
is the germ of magnetic and electric energy from which 
the full power of the machine is derived. 

When the armature begins to revolve, and its coils 
intercept the lines of force from this residual magne¬ 
tism, found in the field, incipient electric currents are 
generated in them, which, having been commuted into 
a single direct current and taken up by the brushes, 
circulate through the coils of the field-magnets. These 
incipient currents induce magnetism in the cores, and 
thus increase the magnetic intensity of the field, so that 
the armature coils intercept an increased number of 
lines of force. This increases the magnetism of the 
armature core, inducing greater energy in the electric 
currents generated; and these currents, passing into the 
field-magnet coils as before, continue to increase the 
magnetic intensity of the field. Thus, magnetism aug¬ 
ments electricity, and electricity reacts to augment 
magnetism; and this series of reciprocal reactions 
between the armature and the field - magnets, and 
between the magnetism induced in the cores of each 
and the electricity induced in their coils, increases the 
magnetic and electric intensity of each in geometrical 
ratio, so that in a few moments the incipient current, 
induced by the feeble germ of residual magnetism, has 
become the powerful current which produces from a 
series of arc lamps a light of 100,000 candle-power. 

When a dynamo stops running, its electric and mag- 


PRINCIPLES OF THE DYNAMO. 


33 


netic energy cease, but it still retains the residual; so 
that, when put in operation again, its energy is rapidly 
developed, and the electric current generated as in the 
first instance. 

It is evident from the manner of electric development 
as described above, that the electric energy generated 
must vary as the speed of rotation of the armature, so 
that the more rapid the rotation, the greater the energy 
developed. But there are certain limits which cannot 
be exceeded, dependent chiefly on the strength of 
material and the incidental development of heat. If 
the limit ol strength is exceeded, the armature is liable 
to fly in pieces; and if too much heat is developed, the 
insulating material may be charred and permanently 
injured, or the electric and magnetic properties of the 
metals be temporarily reduced. The development of a 
certain amount of heat is inevitable, and it varies in 
different dynamos according to the method of construc¬ 
tion. Hence the adjustment of speed in each case 
becomes an important item. Taking the number of 
feet in the circumference as a basis, the rate of speed 
in most dynamos varies from two to three thousand feet 
per minute, while in some it equals five thousand ; that 
is, that number of feet of circumference passes a given 
point in a minute ; and the number of revolutions per 
minute, in any case, can be ascertained by dividing by 
the number of feet in the given circumference. 

To the ordinary observer, not versed in electric 
science, and especially to the mechanic, accustomed to 
visible, tangible resistance requiring power to over¬ 
come it, the resistance ol the dynamo is a profound 
mystery. Here is an armature capable of being put in 
rotation by a few pounds pressure applied with the 


34 


THE ELEMENTS OF ELECTRIC LIGHTING. 


hand, and rotating apparently in empty space; but 
through some invisible agency the resistance increases 
with the speed, till, in a few moments, an engine of a 
hundred horse-power is required to sustain the rotation. 
But this apparently empty space is the magnetic field 
through which radiate an infinite number of lines of 
force, cut by the armature coils, and generating the 
electric current in the manner described; so that 
the resistance, though invisible, is as real as that of the 
machinery of a factory. It is, in this respect, a resist¬ 
ance similar to that of gravity, unseen, intangible, yet 
real. 

Series Shunt and Compound Winding. —Dynamos 
are divided into three classes, according to the method in 
which the field-magnets are wound and the relations of 
this winding to the external circuit, known respectively 
as series , shunt , and compound wound. In the series 
wound dynamo, illustrated by Fig. 5, the entire current 
traverses a single route of low resistance, passing in series 
through the armature coils, field-magnet coils, and ex¬ 
ternal circuit, back to the armature; so that any varia¬ 
tion of resistance, at any point, as by the introduction 
of a lamp or otherwise, affects the whole series equally ; 
the current strength varying inversely as the resist¬ 
ance. 

In the shunt winding, illustrated by Fig. 10, two dis¬ 
tinct circuits are provided, an external circuit of coarse 
wire, and hence of low resistance, and a shunt circuit 
of fine wire and high resistance, wound on the field- 
magnets. The current divides at the upper brush in the 
inverse ratio of the resistance of each circuit, 1J# to 20^ 
traversing the shunt and employed exclusively to excite 
the field magnets, while the main current flows through 


PRINCIPLES OF THE DYNAMO. 


35 


the external circuit and is employed for useful work, as 
the production of light. 

If the resistance of the external circuit is increased, as 
by the introduction of a lamp, the strength of its current 
is proportionately diminished; but the potential differ- 



Fig. 10. 


ence, or electromotive force, between the brushes, repre¬ 
senting the electric pressure, is increased by the dimin¬ 
ished flow of current in the ratio this increased resistance 
bears to itself plus the armature’s resistance: and as the 
resistance of the shunt remains constant, the strength of 
its current is proportionally increased by this increase 
of electromotive force; and the magnetism of the core 















































































































36 THE elements of electric lighting. 

being increased in the inverse ratio of its magnetic 
saturation by this increase of current strength in the 
shunt, its reaction increases the current strength in both 
circuits, thus supplying electric energy to overcome the 
increased resistance. By this series of adjustments an 
equilibrium between these various factors is established, 
the total electric energy developed varying as the 
mechanical energy expended. Decrease of external re¬ 
sistance reverses these results. 

This increase of current strength in the shunt is rela¬ 
tively small as compared with decrease of that in the ex¬ 
ternal circuit. Current is not diverted from one branch 
to the other, which would imply that the strength of the 
shunt current is increased to the same amount as that of 
the external circuit is diminished, but varies as the rela¬ 
tive conditions of resistance and electromotive force vary 
with respect to the relative capacity of each branch of 
the circuit. The resistance of the shunt may be varied 
as required by resistance coils. 

The compound winding, illustrated by Fig. 11, is a 
combination of the series and shunt methods; a shunt 
circuit of tine wire and high resistance being employed 
exclusively to excite the field-magnets, while a coarse 
wire circuit, of low resistance, is also employed for the 
same purpose, and connected with the external circuit, as 
in the series method. The automatic regulation is sim¬ 
ilar to that of the exclusive shunt method, except that 
the entire current flows through the field-magnet coils. 
This method is susceptible of very delicate adjustment 
and regulation by adjusting the relative resistances of the 
two circuits. 

Each of these three methods of winding has its special 
adaptation to the requirements of a certain kind of work. 


PRINCIPLES OF THE DYNAMO. 


37 

Iii electric lighting it is found that the series wound dy¬ 
namo is usually the most suitable for arc lighting, and 
the shunt and compound wound for incandescent light¬ 
ing; arc lighting requiring high electromotive force and 
comnaratively small current, while the requirements for 



Fig. 11. 


incandescent lighting are the reverse: which leads to the 
classification given below. 

Constant Current Dynamo. —To maintain a number 
of arc lamps, connected in series, at a given illumination, 
a constant current flowing from lamp to lamp is required 
for each. If but one lamp were lighted the required 












































































































































38 


THE ELEMENTS OF ELECTRIC LIGHTING. 


electromotive force, or potential, would be comparatively 
small; but if two were lighted, the resistance being 
doubled, the electromotive force must be doubled to 
maintain the same current strength; and the same ratio 
of electromotive force to resistance must be maintained 
for any number lighted or extinguished. 

Hence the construction and regulation of a dynamo 
for such work must be such as to furnish electromotive 
force capable of variation within the required range; 
and a machine so constructed is known as a constant 
current dynamo, and is usually series wound, as stated 
above. 

Constant Potential Dynamo.— But if the required 
work were the maintenance of a number of incandescent 
lamps connected in parallel, the lamps being on branches 
derived from the main circuit, the variation of resistance 
is confined to these branches, in which it becomes ad¬ 
justed to the requirements of the current, the resistance 
of the main circuit remaining constant; hence the 
electromotive force remains nearly constant, and a ma¬ 
chine adapted to such work is known as a constant 
potential dynamo, and is either shunt or compound 
wound. 

Direct Current and Alternating Current Dyna¬ 
mos. —Dynamos are divided, according to the nature of 
the current generated, into two classes, the direct cur¬ 
rent and alternating current, according as the current 
flows continuously in one direction, or alternately in 
opposite directions. For some purposes, especially that 
of electroplating, a continuous current in one direction 
is an absolute necessity, as a reversed current would, in 
this case, remove the metal deposited by the direct cur- 


PRINCIPLES OF THE DYNAMO. 


39 


rent; but in electric lighting, it is a matter of less con¬ 
sequence, continuity and steadiness being of more im¬ 
portance than direction of current. 

It has already been shown that the continuous cur¬ 
rent is made up of a succession of transient, momen¬ 
tary currents collected into one; and that, by means of 
the commutator, these are all made to flow in the same 
direction. But for the purpose of continuity, it is 
immater ial whether these momentary currents are in 
the same direction or in opposite directions, provided 
there is no perceptible break between them. The case 
is analogous to that of a circular movement as com- 
pared Avitli an oscillating movement in mechanics i the 
rapidity of movement in each case may be such that the 
eye can not distinguish between the separate impulses, 
so that the oscillating may appear as continuous as the 
circular. 








CHAPTER III. 

Direct Current Dynamos. 


Direct current dynamos are divided according to the 
number of poles in the field-magnet into two classes, 
known respectively as bipolar and multipolar; the bi¬ 
polar having only two field-poles, and the multipolar any 
number more than two. A few leading dynamos of each 
('lass will illustrate the different methods of construction; 
and the bipolar being the simplest, and the type employed 
in illustration of the principles of the dynamo, in the pre¬ 
vious chapter, may appropriately he described first. 

The Excelsior Dynamo. —This dynamo, as recently 
improved by its original inventor, William Ilochhausen, 
is shown in Figs. 12 and 13, which represent the largest 
size made, capable of lighting 100 arc lamps, of 2000 
candle-power eacl i. 

Its armature core is constructed of iron wire, wound 
on a cast-iron frame having a T section which divides it 
into two equal parts, as viewed edgewise. This core is 
mounted on a spider attached to the shaft, the arms of 
which are insulated from the core. The armature is of 
the Gramme, or ring, type, and, in machines of the size 
here shown, is 30 inches in diameter and 8 inches thick, 
and has 160 pounds of No. 16 insulated copper wire 
wound on its core, in 36 coils as shown. These coils are 
rectangular, each being 8 inches square, and are sepa- 

40 



DTUECT CURRENT DYNAMO. 


41 


rated from each other by wooden wedges attached to the 
cast-iron frame, to the outer ends of which are screwed 
blocks of insulating fibre which hold the coils in position. 



Fig. 12. 


The field-magnet consists of a vertical cast-iron yoke, 
connecting two horizontal cast-iron cores, on which are 
wound 1300 pounds of hfo. 8 insulated copper wire, hr 
two coils, connected in series with the armature and ex¬ 
ternal circuit. Each of these coils is divided into two 



































































































































































































































42 


THE ELEMENTS OF ELECTRIC LIGHTING 
























































































































































DIRECT CURRENT DYNAMOS 


43 


sections as shown; and each front section is tapped at 
equal intervals by 10 wires, making 20 subsections in the 
two, which are connected by these wires with a field- 
switch which forms part of the system of automatic regu¬ 
lation described hereafter. 

The armature is supported on interior hearings, not 
shown in the cuts, and is partly inclosed by the cast-iron 
pole-pieces attached to the magnet cores. Each of these 
pole-pieces is made in two sections, hinged together so 



Fig. 14. 

that they can he opened, as shown in Fig. 13, to allow 
the armature to he drawn out for repairs, without remov¬ 
ing the shaft from its bearings. To the outer section of 
each pole-piece is bolted a curved arm ; the upper arm 
supporting the brushes and part of the regulating appa¬ 
ratus, as shown in Fig. 13; these arms being" bolted 
together when closed, as in Fig. 12. 

The commutator consists of the usual copper seg¬ 
ments, to each of which is attached an arm, at right 
angles, as shown in Fig. 14; and these arms are bolted 
to a marble disk inclosed by a copper band; so that the 
segments are insulated from each other by air spaces in- 























44 


THE ELEMENTS OF ELECTRIC LIGHTING. 


stead of the usual solid insulating material, and the sup¬ 
porting arms by the marble. This construction gives 
the commutator the best possible interior ventilation ; the 
segments projecting into the air, without interior sup¬ 
port, so that it is impossible for it to be injured by 
heating; and also allows any segment to he removed for 
repairs without disturbing the others. 

The automatic regulation of this dynamo is one of its 
most notable features. It is controlled by a small motor, 
inclosed in the circidar box shown at O in Fig. 12, which 
is attached to the upper curved arm. These arms are 
insulated from the pole-pieces by hard-rubber, so that 
only a small number of the magnetic lines of force trav¬ 
erse them; barely enough to create a magnetic held of 
sufficient strength for the operation of this little motor, 
without serious reduction of the strength of the main 
held in which the armature of the dynamo revolves. 
This motor is constructed with a little armature, shown 
in Fig. 15, which rotates in this held, and is connected 
with the electric circuit of the dynamo by two little 
brushes, from which conducting wires extend to a con¬ 
trolling electromagnet M M, and resistance coils of Ger¬ 
man silver wire R 1 IV R 8 , contained in a case attached 
to the wall; this part of the apparatus being known as 
the wall controller. 

This apparatus regulates the electric current not only 
by moving the main brushes on the commutator to or 
from the neutral line, but also by increasing or decreasing 
the number of sections of the held coils through which 
this current is flowing; cutting out sections as the brushes 
are moved from the neutral line, and thus reducing the 
electromagnetic energy of both the held and the arma¬ 
ture, and reversing this operation as the brushes are 


EXTERNAL CIRCUIT 








































































































































40 


THE ELEMENTS OF ELECTRIC LIGHTING. 


moved toward tlie neutral line, and thus increasing this 
energy. 

The manner in which this is accomplished will be un¬ 
derstood by an examination of the diagram shown in Fig. 
15, in which an outline of the field-magnets with the 20 
wires connecting the coil sections with a sliding field 
switch is shown on the left below, and the commutator 
and motor regulator on tl le right; all connected with the 
wall controller above, and with the external circuit. 

It will be noticed that the little motor is geared by a 
curved rack to a yoke or rocker to which are attached 
the main brnshes M B M B, and that the rod F F, which 
operates the field switch S, is connected with this rocker 
by a vertical arm; therefore as the main brushes are 
moved from the neutral line, the upper to tl le left and 
the lower to the right, the field switch S is pulled down, 
cutting out sections of the field coils; but when the move¬ 
ment of the brushes is in the opposite direction this action 
is reversed. 

Following the course of the current as indicated by 
the arrows, we find that it passes from the upper field- 
magnet coils through the top inside wire, positive ter¬ 
minal P 4, binding-post 4 in wall controller, coils of 
electromagnet M M, hinged lever armature A, resistance 
coil It 1 , binding-post 1, line and external circuit, to neg¬ 
ative terminal N 1, upper main brush M B, through the 
armature coils to lower main brush M B, and thence 
by terminal at S 2 to bottom inside wire and lower field- 
magnet coils. 

The lever armature A, when perfectly horizontal, as 
shown, rests on two contact points C and C 1 , attached to 
the lever B, and remains in this position so long as the 
current which traverses the magnet M M remains at its 


DIRECT CURRENT DYNAMOS. 


47 


normal strength; but when the strength of this current 
rises above the normal, the magnetism being increased, 
the armature is attracted downward in opposition to the 
force of the spiral springs shown, and the contact at C 
opened while that at C 1 remains closed. But if the cur¬ 
rent strength falls below the normal, the magnetic at¬ 
traction being weakened, the armature and lever B are 
pulled upward by the springs, above the horizontal posi¬ 
tion, and the contact at C 1 is opened while that at C 
remains closed. 

These two contact points are connected with the 
brushes of the little motor below by two wires which 
pass upward through the posts 2 and 3, and thence 
downward to the motor brushes through terminals 2 and 
3. These wires are tapped at P 2 and P 3 by the resist¬ 
ance coils R 2 and R 3 , which connect them with the line 
and external circuit. Part of the main current can flow 
through the contact points C or C 1 to the motor, when 
one contact is open and the other closed; but when both 
are closed, the E. M. F., or electric pressure, being equal 
in both wires, and opposite in direction, there can be no 
current, since there is no difference of potential. 

When therefore the main current rises above its nor¬ 
mal strength, the armature A being attracted and the 
contact at C opened, part of the current is shunted 
through C 1 to the motor by post 2 and terminal 2, and 
entering by the left hand brush traverses the motor 5 s 
armature and returns from the right hand brush through 
3, 3, P 3 , and resistance coil R 2 , to the line. This causes 
the armature of the motor to rotate in such direction as 
to move the main brushes M B M B from the neutral 
line by means of the rocker, and also cut out sections of 
the field coils by means of the field switch S, moved by 


48 


THE ELEMENTS OF ELECTRIC LIGHTING. 


the rod F F, thereby reducing the current to its normal 
strength. But when the main current falls below its 
normal strength, the contact C 1 being opened, the shunt 
current passes from C, through 3, 3, to the right hand 
brush of the motor, and traversing the motor’s armature 
in the opposite direction, reverses its rotation, thereby 
moving the main brushes toward the neutral line, and 
reversing the movement of the field switch, so as to in- 
crease the magnetic energy; and thus restores the current 
to its normal strength. 

The relative quantities of current which traverse the 
shunt and the main circuit are regulated by a proper ad¬ 
justment of the relative resistances of the coils It 1 , IF, 
and B/\ And the movements of the armature A are regu¬ 
lated by a proper adjustment of the relative strength of 
the magnetic attraction of the magnet M M and of the 
spiral springs which oppose it. 

By means of the switch S 1 , the motor may be cut out 
of the circuit while adjusting the magnet M M. And 
the switch S 2 is employed to produce a short circuit 
between the lower and upper halves of the held magnet 
when stopping the dynamo. 

The Brush Dynamo. —The distinctive features of the 
Brush dynamo relate chiefly to the construction of the 
armature and commutator. The armature core, shown 
at A", Fig. 16, has a central ring, B, B , B , composed 
of layers of thin sheet iron ribbon, insulated by vul¬ 
canized fiber. These are separated from each other 
by short iron pieces, one of which is shown at T; the 
central part of each having the same width as the 
ring, while at each end are projections on opposite 
sides, forming, when placed in the core, the V-shaped 
figures shown at X; the arrangement, when the core is 


DIRECT CURRENT DYNAMOS. 


49 


bolted together, being shown in cross-section at Z. 
The ends of these pieces are separated slightly in the 
interior, and more widely at intervals in the exterior, 
as shown in Fig. 17. The core is bolted to an interior 
rim, shown in Fig. 17, which is attached at four opposite 
points to a spider mounted on the shaft. 

Phis open, laminated structure affords ventilation, 
eliminates the Foucault currents, and gives, in the 



z y 

Fig .16. 


central portion, between the projections, a solid support 
for the coils. The old-style core, which resembles this, 
was of cast-iron, deeply channelled for ventilation, in 
the center and in each projection, but was abandoned 
on account of the Foucault currents and consequent 
heating, notwithstanding the excellent ventilation. The 
new core gives the dynamo an increase of more than 
forty per cent in efficiency. 






























50 


THE ELEMENTS OF ELECTHIC LIGHTING. 


The coils are wound with insulated copper wire be¬ 
tween the projections, as shown in Fig. IT, and sup¬ 
ported on the exterior and interior portions of the core 
by projecting flanges. The winding is of the open 
circuit type described on page 18, the coils . being 



Fig. 17. 


arranged in pairs on opposite sides of the armature, 
each pair forming a complete, independent circuit, the 
two ends of the wire being attached to opposite seg¬ 
ments of the commutator ; an eight-coil armature having 
four circuits and eight commutator segments, as shown 
in Fig. 18, in which the connections with the commu¬ 
tator are represented, that part of the wire connecting 
each pair of coils being omitted. 









DlliECT (JURliENT I) YNAMOS. 


51 


The construction of the commutator and. its connec¬ 
tion with the coils will be understood by comparing 
Fig. 18, showing the connection, with Fig. 19, in which 
it is shown in perspective. It consists of two cylinders, 
as shown, each having an equal number of segments; 
an eight-part commutator, being composed of two 
four-part cylinders mounted on the same shaft, in such 
a position that the segments on one cylinder are about 
one-eighth of a circumference in advance of those on 
the other; the narrow end of each T-shaped segment 
of one cylinder being placed opposite the broad end of 
each similar segment of the other. In the latest style 
the narrow part of the segment is cut off and replaced 
by a block of lignum vitae, which has a copper strip on 
one edge to prevent wear from the brush contacts ; so 
that each four-part cylinder has, at each end, two seg¬ 
ments placed as shown, with narrow blocks between. 
The segments are of copper, separated by air spaces, 
and screwed to segments of brass mounted on two con¬ 
centric interior cylinders, one of vulcanized fiber, 
immediately under the brass segments, and the other, 
which is attached to the shaft, of lignum vitae. 

It will be seen from Fig. 19, that while the brushes 
A, A\ are each in contact with a single commutator seg¬ 
ment, the brushes B , B\ are each in contact with two 
segments; and by comparing this with Fig. 18, it is seen 
that A, A', are thus connected with coils 3, 3, while B , B\ 
are connected with coils 2, 2, and 4, 4; coils 1, 1, being 
disconnected. B , B', are therefore connected in parallel 
with two pairs of coils, but not with two adjacent pairs, 
coils 3, 3, lying between them. Six of the eight coils 
are thus brought into action at once, and this represents 
the relative positions of the various parts constantly 


THE ELEMENTS OF ELECTRIC LIGHTING 


5 ^ 



Fig. 18. 






Fig. 19. 
































DIRECT CURRENT DYNAMOS. 


53 


during rotation. Coils 3, 3, are in the line of greatest 
variation of magnetic intensity and consequently of 
best action, and are joined through the external circuit 
by the brushes A , A'; coils 4, 4, approaching this 
position, and coils 2, 2, leaving it are joined in parallel 
by the brushes B , B'; while coils 1, 1, being in the line 
of least variation of magnetic intensity, and conse¬ 
quently of least action, are disconnected. The current 
from the external circuit entering at A and traversing 
coils 3, 3, leaves at A', thence returns through the ex¬ 
ternal circuit to B, and traverses coils 2, 2, and 4, 4, 
leaving by the external circuit at B\ and thence returns 
again to A, completing the circuit. It is thus seen that 
the positive current is from coils 3, 3, where the electric 
potential is highest, to coils 2, 2, and 4, 4, of lower 
potential, from their position, and of less resistance 
from being joined in parallel, and thence negatively 
back to 3, 3. 

It is evident that such an armature may be composed 
of any even number of coils, arranged as described. 
The armature of the largest Brush dynamo has sixteen 
coils. The copper segments of the commutator are 
attached with screws, and easily removed for repairs or 
renewal. 

Two styles of the Brush dynamo are now made, one 
for arc lighting, series wound as formerly, and the other 
compound wound for incandescent lighting. The auto¬ 
matic, rotary movement ol the brushes on the commuta¬ 
tor, already referred to, has been recently adopted, and is 
used in both machines. The arc-light machine is shown 
in Fig. 20. The field-magnets, which are of the horse¬ 
shoe type, are placed on opposite sides of the armature as 
shown. Those of the arc-light dynamo are wound with 


iA 


the elements of electetc lighting 


















































DIRECT CURRENT D TNAMOS. 


55 


large wire, and have also an interior tine wire used as a 
slmnt in regulating the lamps. The magnets of the 
compound wound dynamo have large wire next the pole- 
pieces, and tine wire next the magnet yokes. It will 
be noticed that the planes of the armature coils are at 


right angles to the plane of rotation, and cut the lines of 
force in a different manner from any of the dynamos 
thus far described; and that the core projections, com¬ 
ing close to the pole-pieces, lead the magnetism through 
the coils. 


The E. M. F. is regulated by a device consisting of 
clutches, gearing, and pulleys, operated by an electro¬ 
magnetic wall controller, through which a small fraction 
of the current is shunted. The position of the brushes 
on the commutator is shifted automatically by this device, 
as the number of arc lamps supplied simultaneously with 
current varies; and thus constancy of current is main¬ 
tained through each lamp, by varying the E. M. F. in 
the same proportion as the electric resistance of the lamp 
circuit varies. 

The Thomson-Hotjston Dynamo. —This dynamo has 
a very peculiar construction. Its armature, shown in 
Fig. 21, is nearly spherical. The armature core, shown 
* in Fig. 22, consists of two cast-iron flanges, G, G , the one 
on the left shown in elevation, and the one on the right 
in section. These are attached to the shaft, and con¬ 
nected by twelve cast-iron ribs, I), 1), as shown, sup¬ 
ported by the flanges, hut insulated from them. These 
ribs are over-wound with several layers of annealed 
iron wire, coated with shellac, Ailing the exterior space 
between the flanges, as shown at I. At the ends and 
center of each rib are inserted projecting wooden plugs, 
shown at 1 J : 1 J ', thirty-six in all, designed to sustain 



56 


THE ELEMENTS OF ELECTRIC LIGHTING. 


the coils in position. The core thus constructed is cov¬ 
ered with several thicknesses of paper for insulation. 
The three coils, composed of insulated copper wire, form 
an open circuit and are connected with a copper ring 
at «, Fig. 21 ; and each of them, starting from this 



Fig. 21. 


ring at distances apart of one hundred and twenty de¬ 
grees, are wound between the wooden plugs over the 
core in the direction of its axis, as shown, in the follow¬ 
ing order: 1. First half of first coil. 2. First half of 
second coil. 3. Whole of third coil. 4. Second half 



of second coil. 5. Second half of first coil. In this 
way each coil is placed at the same average distance 
from the core. When the winding is completed, the 
free ends of the three coils, shown at f, are led through 
an opening in the shaft, and attached to the three seg¬ 
ments of the commutator, and the armature is bound 























































DIRECT CURRENT DYNAMOS. 


57 


together in the usual manner by bands of brass wire 
shown at b l>, d d. 



The ring armature, shown in Fig. 23, is now used on 
machines of the larger size. It is constructed with a 
laminated core mounted on two gun-metal spiders, bolted 
together and supported on opposite ends of the shaft, 
and removable for repairs of the coils. 

There are thirty coils, arranged in six sets of live coils 




































58 


THE ELEMENTS OF ELECTRIC LIGHTING 


each, as shown; each coil being* shaped as shown in Fig*. 
24, constructed of insulated copper wire, wound sepa¬ 
rately on a form before being placed on the core, and 
covered with insulating tape on the lower parts and ends. 
They are separated from each other on the inner part of 
the ring by strips of wood, and on the outer part by 
wooden blocks placed under the central wire band, and 
the live coils of each set are connected together by their 
terminals in grooves in these blocks. 

The sets on opposite sides of the ring are cross-con¬ 
nected at the pulley end by their terminals, in three 
pairs, as shown at 13 in Fig. 25; set 1 being thus con- 



Pig. 


24. 


nected to set 1', set 2 to set 2', and set 3 to set 3'; these 
connections being made on a wooden disk. Three of the 
six remaining terminals are connected at the commutator 
end, to a copper ring, as shown at A, and the other 
three, alternating with them, are brought out through a 
tube, as shown in Fig. 23, and connected with the three 
commutator segments; the terminals of sets 1, 2, and 3 
being connected with the commutator segments, and 
those of F, 2', and 3' with the ring. 

Hence the current entering the armature from the 
lamp circuit by the lower pair of brushes and commuta- 





DIRECT CURRENT D YNAMOS. 


59 


tor segment, traverses the coils connected with that seg¬ 
ment, and returns by the cross-connection and opposite 
set to the ring, where it divides, the two halves going to 
the other two sets of coils connected with the ring*, and 
* returning through the cross-connections and opposite sets 
to the other two segments of the commutator, and 
thence through the upper pair of brushes to the lamp 
circuit. 

At the next half revolution of the armature this order 
is reversed, the current, entering as before by the lower 
pair of brushes, is divided between two commutator seg¬ 
ments, as shown in Fig. 25, at A and B, instead of being 
united on one, traverses the two sets of coils connected 
with them, and returns to the ring by the cross-connec- 
tions and two opposite sets, where the two currents unite 
and return from the ring by the other set of coils and 
cross-connection to the remaining commutator segment, 
as shown at A, and thence through the upper pair of 
brushes to the lamp circuit, as before. 

The ring armature can be substituted for the old style 
armature in machines of the same size, but many still 
prefer the old style. 

The field-magnets, shown in Fig. 26, are constructed 
with two tubular cast-iron cores, open at the outer 
extremities, and terminating in broad flanges; while the 
inner extremities terminate in spherically concave pole- 
pieces, which nearly inclose the armature, and are 
furnished with brass flanges, between which and the 
outer flanges the magnet coils are wound, as shown at 
C and O'. These two cores are bolted together by 
bars of soft wrought-iron, b , b , connecting the outer 
flanges, forming virtually, when wound, one magnet, 
its poles facing each other in the center where the 


60 


THE ELEMENTS OF ELECTRIC LIGHTING. 


COMMUTATOR END 



PULLEY END 













DIRECT CURRENT DYNAMOS, 


61 

armature revolves. The pole-pieces being inclosed 
within the magnet coils, and the armature brought into 
immediate contiguity with them, there is an increase of 
magnetic intensity upon the armature, which is inversely 
proportional to this reduction of distance, and conse¬ 
quently much greater than if the pole-pieces projected 
in the usual manner. The pole-pieces, being spherically 
concave, concentrate the magnetism of the field upon 
the spherical armature by radiation towards its center. 
The magnets of the arc-light machines are series wound 
with No. 12 insulated copper wire; those of the incan¬ 
descent-light machines are compound wound, the fine 
wire of the shunt covering the tubular part of each 
core, while the coarse wire is wound in a peculiar 
manner close to the pole-pieces, and separated from 
the fine wire by the projecting flanges: hence both 
circuits excite the field-magnets, and, being joined at 
the brushes, their currents traverse the armature coils. 

There are two pairs of brushes which bear on the 
commutator in the manner shown in Fig. 27; these, as 
shown in the perspective view of the dynamo, Fig. 26, 
are attached to a yoke, and controlled by a magneto¬ 
electric regulator placed in the circuit, and mounted on 
the supporting frame of the dynamo, as shown at the 
left. By the operation of this regulator the brushes of 
each pair are drawn together or separated, as shown in 
Fig. 27, and the current increased or diminished as re- 
quired, by increase or decrease of the electromotive force 
produced in this manner. The rotation being in the direc¬ 
tion of the external arrows, m m represents the neutral 
line, and the internal arrows represent the direction 
of the current; consequently when the brushes occupy 


02 


THE ELEMENTS 


OF ELECTRIC LIGHTING . 


































DIRECT CURRENT D YNAMOS . 


63 


positions near this line, as at P F, and P f F', the 
electromotive force is greater than when they recede 
from it to the positions p, 
f\ and p',f. In the first 
position the brushes of each 
pair being 60 degrees apart, 
and the length of each com¬ 
mutator segment being a 
little less than 120 degrees, 
the two brushes of one pair 
always bear on one segment, 
while each brush of the op¬ 
posite pair bears on a sepa¬ 
rate segment; so that two 
coils are always in parallel, and are in series with the third 
coil, as shown. The electromotive force, under these 
conditions, must always be greater than when the 
brushes occupy the second position, the brushes being 
nearer the neutral line, ai d the time of contact with 
each segment in this best position being thus pro¬ 
longed. But when they recede to the second position, 
they are farther removed from the neutral line, the 
time of best action is reduced, and, six times in each 
rotation, two opposite brushes momentarily touch the 
same segment, and are thus short-circuited. Hence, 
under these conditions, the electromotive force is reduced 
in proportion to the distance apart to which each pair of 
brushes is separated. When from a reduction of resist¬ 
ance in the lamp circuit by the extinguishing of a 
lamp, or otherwise, the current feeding the remaining 
lamps becomes liable to an abnormal increase, this 
increase is shunted through a very sensitive electro¬ 
magnet, termed the controller magnet, connected with 



u 


THE ELEMENTS OF ELECTRIC LIGHTING. 


the regulator magnet of the dynamo, already referred to : 
the armature of the regulator is attracted, the lever con¬ 
necting with the brushes is raised, the brushes separated, 
and the current reduced. When, from an increase of 
resistance in the lamp circuit, the current is diminished, 
this operation is reversed; the brushes drawn closer 
together, and the current increased; the brushes 
being so adjusted that one commutator segment is out 
of connection during each revolution. By this method 
constancy of current under varying resistance is main¬ 
tained, the electromotive force being made to vary as tho 
resistance. This system of automatic regulation, vari¬ 
ously modified, is practically the same as that in use in 
other dynamos already described. 

One striking peculiarity of this dynamo is the air- 
blast spark-controller, — a mechanical contrivance by 
which air is blown against the brushes at their points 
of contact with the commutator, by which means spark¬ 
ing at these points is suppressed. 


It is shown in position in Fig. 26, just back of the 
commutator, and in detail in Fig. 28, and is constructed 
with a circular iron box, shown at A, which incloses a 
hard-rubber box, having an elliptic shaped interior in 
which a three winged blower rotates. The wimrs fit 
loosely in slots, and are driven out against the inclosing 
rim by centrifugal force, at the wide parts of the ellipse, 
and pushed in by contact with this rim, at the narrow 
parts; so that they are constantly in contact with the 
rim. The air is drawn in through two grated openings, 
on opposite sides at the narrow parts, accumulates in 
the wide parts, and is expelled against the brush con¬ 
tacts through two air jets which lit the circular holes 


DIRECT CURRENT DYNAMOS. 


65 

shown at opposite sides; one of these jets being shown 
separately at 13. 

The three wings operate together, both as air expellers 
and as valves, each wing closing connection with the 
opening which it has passed, while the preceding wing 



opens connection with the one which the former wing is 
approaching, as shown; a partial vacuum being created 
by the expulsion of the air through the jets, into which 
air rushes through the grated openings. 

Sparking at the brushes, due to self-induction in the 
coils of the machine, is the result directly of the 





















































THE ELEVENTH OF ELECTRIC LIGHTING. 


66 


passage of electricity through the air, as the brushes 
change from segment to segment of the commutator 
during its rotation, and some part of a brush is for an in¬ 
stant out of electric connection, all dynamos being more 
or less subject to it. The heat developed at the commu¬ 
tator by friction and electric action rarefies the air, and 
hence reduces its resistance, and increases the liability to 
sparking. Hence, a constant, strong current of cool 
air, such as is supplied by this air blast, increases the 
resistance, and, as the result shows, renders it too great 
tor the passage of the spark. The current theory that 
the spark may be u blown out,’ 5 in the same sense as a 
light is extinguished in ordinary combustion, is not 
strictly accurate. In ordinary combustion the blast re¬ 
moves the burning gas and combustion ceases, but, in 
this case, it removes air of low resistance and replaces it 
gli resistance, and also keeps the brushes and 
commutator cool, and hence the air surrounding them. 
The arc-light may also be extinguished by a blast of air, 
and is more nearly a parallel case. But, in the arc, the 
electiic current is maintained after the separation of 
the carbons by the conductivity of the burning carbon 
' and the blast extinguishes it by removing this vapor 
and thus increasing the electric resistance, so that the 
cuirent cannot traverse the intervening air spacer 
whereas, in sparking at the brushes, there is no combus¬ 
tion or burning vapor, but simply air heated to incandes¬ 
cence. 

With the air blast, oil can be freely used to reduce the 
wear on the brushes without affecting the insulation. 

The lightning arrester, used to protect the dvnamo 


DIRECT CURRENT D YXAMOS. 


L* *7 

b< 


against damage by lightning, is also an important adjunct. 
It is shown in Fig. 29, and is constructed with an electro¬ 
magnet, through the coils of which the current between 
the lamp circuit and dynamo passes. The two magnet 
cores project vertically above the coils, as shown; and 
between them are placed, edge to edge, two projecting 
wings of brass, their broad bases about one-fourth of an 
inch apart, and their narrow upper parts receding from 
each other, as shown. 

The instrument is 
mounted on a wooden 
base, screwed to the 
wall; and the wings are 
out of contact with the 
magnet cores, each one 
screwed to a brass lug, 
one of which is connect¬ 
ed with a line leading 
to the lamp circuit, and 
the other with a Xo. 4 
copper wire leading to 
the earth, as indicated. 

The line from the dyna¬ 
mo circulates round the 
magnets, and is also con¬ 
nected to the upper 

right-hand lug. The lamp circuit line has thus two 
branches from this lug, one through the magnet to the 
dynamo, and the other through the brass wings to the 
earth; the latter interrupted by the narrow, quarter-inch 
air space at the base of the wings. This air space is suf¬ 
ficient to insulate the left wing from the dynamo cur¬ 
rent; but if a discharge of lightning occurs on the line. 



Fig. 29. 





















































































































































THE ELEMENTS OF ELECTRIC LIGHTING. 


r»8 


its great intensity causes it to leap the air space, and 
take the shortest course to the earth; the projecting 
edges of the wings facilitating the discharge, though not 
sharp enough to short-circuit the dynamo current. Part 
of the discharge must go to the dynamo, dividing be¬ 
tween the two branches in proportion to the relative 
resistance of each; hut the distribution of this portion in 
the mass of the machine prevents in jurious results. 

The object of the projecting magnetic poles, between 

which the wings are 
placed, is to extinguish 
the spark during the 
passage of the discharge 
from wing to wing, by 
establishing a magnetic 
current at right angles 

O o 

to the line of discharge. 

Fig. 30 shows the rel¬ 
ative positions and con¬ 
nections of the various 
parts of the system; 
two arresters, one in each 
branch of the circuit, 


Ciwurr 



being recommended as shown. 

Various kinds of arresters are used in connection with 
different systems of electric lighting, in some of which 
combs with projecting teeth take the place of the wings, 
in others a soft metal connection is melted; while in 
others a mechanical device, operated electrically, severs 
connection with the machine. These arresters are also 
applicable to telegraph and telephone systems, and are 
applied in a similar manner. 
































DIRECT CURRENT DYNAMOS f>9 

1 he A\ ood Dynamo.— This dynamo will be readily 



Pig. 31. 

understood from Figure 31, without any detailed de¬ 
scription. It is of the Gramme type, embracing the 














































































































70 


T1IK ELEMENTS OF ELECTRIC LIGHTING. 


features of ventilation of tlie armature, and automatic 
current regulation, hut presenting nothing in its con- 



Pig. 32. 


struction which has not already been fully described, 
except the current regulator. This is illustrated by 
Figs. 32 and 33. Fig. 32 is an end view of the dynamo, 








































































































































































































































































































DIRECT CURRENT DYNAMOS 


71 


showing the apparatus in full 
of the same end, showing 


; and Fig. 33 a side view 
the connection with the 



brushes ; the automatic shifting of the brushes on 
the commutator to vary the electromotive force being 
the object to be accomplished. lhe large friction 



























































































































72 


THE ELEMENTS OF ELECTHTC LIGHTING. 


wheel shown in Fig. 82 has a broad rim with a 
deep groove on its inner surface next the dynamo. 
The end of the armature shaft fits loosely into this 
groove, as shown by the dotted circle on its right side, 
but is out of contact with the wheel in the normal 
state of the current. This friction wheel is connected 
at its centre with the short arm of the curved lever 
shown in the cut. Above the lever on the right is 
shown an electro-magnet, connected with the lamp cir¬ 
cuit, the armature of which is attached to the long arm 
of the lever; and below it is a spiral spring which acts 
against the magnetic attraction. Two stops at the ex¬ 
tremity of the long arm limit its movement; and a dash- 
pot, which consists of a piston moving in a cylinder 
against air, or other resistance, steadies the movement, 
and makes it gradual instead of impulsive. A pinion 
on the hub of the friction wheel engages gearing con¬ 
nected with the yoke to which the brushes are attached, 
as shown in Fig. 38. The magnetic attraction acting 
against the retractile force of the spring is just suffi¬ 
cient, in the normal state of the current, to hold the 
lever in such a position as to keep the friction wheel 
out of contact with the revolving armature shaft. An 
abnormal increase of current strength increases the mag¬ 
netic force, which attracts the armature, and raises the 
lever, which presses the friction wheel against the revolv¬ 
ing shaft on one side of the groove, and by means of the 
gearing causes the brushes to recede from the neutral 
line. An abnormal decrease of current lessens the mao-- 
netic attraction, the lever is drawn down by the spring- 
the friction wheel pressed against the opposite side of 
the groove, the motion reversed, and' the brushes made 
to approach the neutral line. 


DTRECT CURRENT DYNAMOS- 


73 


The General 


Electric Company’s Multipolar Dy¬ 


namos. —The General Electric Co. makes two different 
kinds of multipolar dynamos for direct connection with 
the source of power, distinguished chiefly by the struct- 



Fi<r. 34. 


ure of their armatures; one kind having iron-dad arma¬ 
tures, and the other kind smooth-body armatures; the 
field-coils in each being either shunt wound or compound 
wound. 

Fig. 3T represents the kind having the ironclad anna- 



































74 


THE ELEMENTS OF ELECTRIC LIGHTING. 


him. This armature, shown separately in Fig. 35, is of the 
drum type. Its core is laminated in the usual manner, de¬ 
scribed on page 16, hut the insulation consists simply of 
japanning on the iron, instead of paper between the disks. 



The armature winding consists of heavy bars of copper 
imbedded in slots on the face of the core; each bar being 
connected with one of the bars next it at one end, and 
with the other at the opposite end, so as to form a single 
continuous coil, wound back and forth between the core 
teeth and round their alternate, adjacent ends. This 
























DIRECT CURRENT DYNAMOS. 


< 0 


coil is insulated with alternate layers of mica and tough 
paper, and its convolutions are connected with the com¬ 
mutator segments by flexible copper strips in the usual 
manner. The armature is ventilated as usual, by air 
spaces between groups of the core disks, which connect 
with interior tubular openings. 

The commutator is mounted on a spider, which is 
bolted to the interior body of the armature, as shown; 
and, in the larger sizes, the clamping ring, which holds 
the segments in place, is made in sections, so that all the 


segments can be secured with equal firmness, and any 
section can he removed to make repairs, without dis¬ 
turbing the others. 


The field-poles, six to twelve in number according to 
the size of the machine, are bolted to a circular yoke 
from which they converge toward the armature, as shown, 
terminating in broad pole-pieces extended on each side 
of the coils. In the maehine here represented, they are 
compound wound, and the coils are divided into two sec¬ 
tions on each pole, as shown. The series coils are on the 
inner sections, and consist of insulated copper ribbon, as 
shown by the connecting terminals between those sec¬ 
tions. The shunt coils occupy the outer sections, and 
also cover the series coils on the inner sections, and are 
composed of wire, as shown. 

The brush-holders are mounted on a spider connected 
with apparatus by which the brushes can all be shifted 
simultaneously on the commutator by turning one of the 
hand-wheels shown, and in the larger machines they can 
also be lifted simultaneously off the commutator by turn¬ 
ing a similar wheel, not shown in this cut. 

The brushes are of the type known as metal gauze, 
and consist of fine wire woven into gauze, and pressed 



TIIE ELEMENTS <)E ELECTRIC LIGHTING. 



Fig. 36 


















DIRECT CURRENT DYNAMOS. 


77 


into the proper shape for brushes. Copper gauze is 
largely used for this purpose, but gauze made of other 
metals is also used, phosphor bronze gauze being pre¬ 
ferred for the brushes of these machines. These brushes 
are noted for their softness, flexibility, and conductivity. 

Fig. 36 represents the machine having the smooth- 
body armature. This armature, shown separately in 
Fig. 37, is of the ring type. Its core, supported on a 
spider, as shown, is laminated and insulated as in the 
ironclad armature. Its winding consists of a single, con¬ 
tinuous coil, constructed of heavy bars of copper, wound 
spirally round the core, and insulated by mica and paper, 
ventilating spaces being left between the convolutions, 
connecting with similar spaces between the core rings. 

The commutator is an integral part of the coil itself, 
being composed of the vertical bars on each side of the 
ring, the outer faces of which, with the insulating mate¬ 
rial between them, are turned perfectly smooth for this 
purpose, after the winding is completed. This gives two 
commutators, one on each side of the vertical face of the 
ring, and when one becomes too much worn for further 
use, the position of the armature can be reversed, and 
the one on the opposite face used. The wear is so very 
slight however, that this is not required for several years. 

The position of the brushes on this commutator is 
shown in Fig. 36, and being all in plain sight, they are 
more easily inspected than those on a horizontal commu¬ 
tator. The same arrangements are made for shifting and 
lifting them simultaneously as in the other machine, and 
they are constructed of the same material. 

The field-coils of this dynamo are all connected with 
the main circuit in parallel; the two terminals of each 
coil being attached to two large wires connected with the 


78 


THE ELEMENTS OF ELECTRIC LIGHTING 


two branches of the main circuit; so that the circuit 
flows across from one wire to the other, in eacli coil sep¬ 
arately, and not from coil to coil in series. This method 



Fig. 37. 

gives much lower E. M. F. than the series method, and 
proportionately increases the volume of the current. 

The pole-pieces, field-cores, and connecting yokes, in 
both these dynamos, are made of soft cast-steel of the 
highest magnetic permeability. The smooth-body anna- 




DIRECT CURRENT DYNAMOS. 


79 


tnres are employed for machines of the largest size, and 
the ironclad armatures for the intermediate and smaller 


sizes. 

In the installment of direct-connected machines of 
either kind in central stations where steam power is em¬ 
ployed, economy of space is effected by running two 
large dynamos of the same kind by an upright steam- 
engine placed between them ; the armatures being 
mounted on opposite ends of the engine shaft, and taking 
the place of the flywheel; thus also employing for use¬ 
ful work the power usually consumed in starting the fly¬ 
wheel and maintaining its momentum. There is also 
an advantage in the perfect uniformity of action obtained 
by running two dynamos of the same size in this way, in 
the tliree-wire system of electric lighting described here¬ 
after. 


The Siemens-ITalske Dynamo, Type I.—Fig. 38 
shows the latest improved dynamo of the Siemens and 
Ilalske Electric Co., the construction of which differs 
materially from that of most other dvnamos now in use; 
leading methods of construction common to other dyna¬ 
mos being reversed. It is a series wound, multipolar 
machine, having four to twelve fleld-poles; the size 
shown in Fig. 38 having twelve, six north poles alter¬ 
nating with six south poles, and generating electric 
energy represented by 1000 liorse-power. 

These poles instead of being attached to an external 
yoke and radiating inward toward the armature in the 
usual manner, are attached to a central sleeve mounted 
on the armature shaft, and radiate outward toward the 
armature. Their cores are composed of soft wrouglit- 
iron, wound, as usual, with insulated copper wire, and fur¬ 
nished with pole-pieces, rounded as shown, to prevent 



80 


THE ELEMENTS OF ELECTRIC LIGHTING. 



mm 


Fig. 38, 






























































































Dili EOT CURRENT DYNAMOS. 


81 


magnetic leakage. This construction reduces the mag¬ 
netic resistance of the field-magnet joke to the minimum, 
hy furnishing the shortest possible magnetic circuit be¬ 
tween the poles, and thus materially reducing the energy 
required to excite the field magnets. 

A ring armature of the Gramme type incloses the field- 
magnets, instead of being inclosed by them in the usual 
manner. It is mounted on a spider the arms of which 
radiate from a central shaft, and have tranverse arms 
attached to their outer ends, at right angles, on which 
the armature is supported as shown. Its core is lami¬ 
nated in the usual manner, being composed of segments of 
sheet-iron perforated with holes for the supporting arms 
to pass through, and lapped at the ends; the rings thus 
formed being insulated from each other with paper, and 
bound firmly together with nuts screwed to the ends of 
the arms. 

The winding of this armature consists of copper bars 
of this shape i i , placed on the inner surface of the 
core, the two short spurs projecting outward on each 
side, and being connected in series with the commutator 
bars which are placed on the outer surface. These spurs 
are attached to opposite ends of adjacent commutator 
bars, so as to form a single, continuous, spiral winding 
all around the armature ring. 

In making these attachments the ends of the commu¬ 
tator bars are slotted, and the ends of the spurs fitted to 
the slots, the projecting ends of the spurs being then 
bent down on the commutator bars, the joints soldered, 
and the surface of the commutator made smooth in a 
lathe. Any commutator bar requiring to be repaired, 
or replaced by a new one, can be removed by unsolder 
ing the joints, without disturbing the other bars. 


82 


THE ELEMENTS OF ELECTRIC LIGHTING. 


Both the spurred hars and the commutator bars are 
thoroughly insulated from each other with mica, asbestos, 
and liber; and ventilating spaces about of an inch 
wide occur between the spurred bars. The entire coil 
is made of the finest, hard-pressed copper. 

This construction reduces the potential difference be¬ 
tween the commutator bars to the minimum, and thus 
prevents sparking at the brushes and consequent injury 
to the commutator by burning. It also reduces the elec¬ 
tric resistance of the armature to the lowest limit by the 
use of a single, massive coil, containing a much greater 
quantity of copper on this large external armature than 
can he used on an internal armature. A most important 
result of this reduction of resistance is the corresponding 
reduction of the heating effect to the minimum; and this 
is further facilitated by the exposure of more than two- 
thirds of the coil’s surface to the air, and by the venti¬ 
lating spaces between its internal bars. So that it is 
quite impossible for this armature to become overheated, 
or to burn out, as sometimes happens to armatures closely 
wound with numerous coils and layers of small cotton- 
covered wire. 

As the generation of electric energy is proportional to 
the number of lines of magnetic force in the field cut by 
the armature coils per unit of time, it is evident that high 
speed of the armature coils is essential to the generation 
of high electric energy. This speed is obtained in arma¬ 
tures of the usual construction, having a limited circum¬ 
ference, by a high rotary speed of the armature shaft; 
but by the greater circumference of this armature, the 
same result is accomplished at a proportionally reduced 
speed of the shaft, the velocity of the coil remaining the 
same. For instance, in an armature having a circum- 


DIRECT CURRENT DYNAMOS. 


83 


ference of 9 feet, and rotating at the rate of 1200 revo¬ 
lutions a minute, any section of the armature coils would 
pass a fixed point at no greater speed than in an arma¬ 
ture having a circumference of 36 feet and rotating at a 
rate of 300 revolutions a minute. Reduction of speed is 
also obtained by the multipolar construction, electric gen¬ 
eration varying approximately as the number of poles. 

This comparatively slow speed of rotation permits the 
direct connection of the armature shaft to the shaft of a 
slow-speed steam-engine or other motor by which the 
rotation of the armature is produced, without the inter¬ 
vention of a belt, with its cost of maintainance, and the 
slipping which produces unsteadiness in the electric light. 

The magnetic attraction of the interior, fixed field- 
magnets, acting in opposition to the centrifugal force of 
the exterior, rotating armature, tends to prevent displace¬ 
ment of the armature’s parts, thus giving this construc¬ 
tion an important advantage over that of an interior, 
rotating armature and exterior, fixed field-magnets, in 
which the magnetic attraction acts in the same direction 
as the centrifugal force. 

It is claimed that the magnetic leakage in a dynamo 

whose armature incloses the field-poles, as in this case, 

is much less than in one whose armature is inclosed by 

the field-poles in the usual manner, since the magnetic 

lines of force are more closely confined to the field 

«/ 

through which the armature coils rotate. 

There are twelve sets of brushes, one set for each field- 
pole. These are mounted on the arms of a spider similar 
to that which supports the armature, and these arms 
radiate from a central sleeve which has a limited rotation 
on the armature shaft. This sleeve is connected with 
gearing operated by a lever, as shown on the left in 


84 


THE ELEMENTS OF ELECTRIC LIGHTING. 


Fig. 88, and the brush-holders are supported in proper 
position over the commutator by a light circular yoke, 
as shown; the positive brushes being insulated from the 
negative. Hence, by a movement of the lever, all the 
brushes can be moved simultaneously on the surface of 
the commutator, to or from the neutral lines, to any 
required distance, till each set occupies, if necessary, the 
position previously occupied by either of the adjacent 
sets. 

The brush-holders are also connected with the hinged 
arms of another spider, which radiate from a sleeve on 
the shaft, and are so arranged that by the movement of 
a lever connected with a rack at, its lower end, as shown 
at the right of the lever already referred to, all the 
brushes can he lifted otf the commutator simultaneously, 
by a rotary movement of the brush-holders at a small 

*1 tl 

angle. Carbon brushes are preferred to copper for 
machines of high E. M. F. 

The armature shaft extends a short distance beyond its 
outer bearing, and this bearing, with the attached brush- 
holder apparatus, can be slid outward to the end of the 
shaft, on sliding ways on which it is mounted, allowing 
the armature to be moved awav from the field-magnets, 
and thus exposing every part of the dynamo for exami¬ 
nation and repairs. 


CHAPTER IV. 


Alternating 


Current Dynamos. 


Thus far we liave confined our attention to the direct 
current dynamo; hut in certain departments of electric 
lighting, the alternating current dynamo is preferred, 
hence its description here is of importance. Fig. 39 
is a fair illustration of the style of construction as 
found in several machines of this class, and shows the 
typical points of difference between these dynamos and 
those we have been considering. Here it will he seen 
that both the armature and the field-magnets are com¬ 
posed of a number of coils, wound on bobbins, and 
attached to the circumference of circular supports. In 
the cut the supporting ring and also the bobbins arc 
omitted from the armature, the coils alone being shown, 
so as to give a better illustration of the movement ot 
the currents. The planes of the armature coils arc 
parallel with those of the field-magnets, and the direc¬ 
tion of rotation parallel to the planes of the coils, the 


axes of the coils being parallel to the axis of rotation. 

By reference to Fig. 39 it will be seen that the north 
and south poles of the field-magnets alternate in posi¬ 
tion, opposite poles facing each other in the usual 
manner. As this causes a reversal of direction in the 
lines of magnetic force between each alternate pair of 
magnets, a corresponding reversal of current is pro¬ 
duced in each alternate coil, as shown by the position 


77/A’ ELEMENTS OF ELECTRIC LIGHTING • 


80 


of the arrows; and as these opposite currents would 
neutralize each other, this again is compensated by a 
reversal in the winding; the wire, as it leaves the 
bottom and front face of one coil, being led over to 
the top and rear face of the next coil, so that the 
momentary armature currents, generated as the coils 
simultaneously pass the field-magnets, all flow in the 
same direction, as shown hy the arrows between the 



Fig. 39. 


coils, while at the next instant this current is reversed, 
as the rotation changes the position of the armature 
coils. So that, following any one coil as it rotates, 
there occur as many reversals as there are pairs of 


field-magnets. 

Instead of the commutator these machines have a col¬ 
lector similarly placed, as shown in Fig. 40, consisting 
of two flat metal rings, mounted on the shaft, and insu¬ 
lated from each other. To these are attached the two 
terminals of the wire composing the coils, as shown 


ALTERNATING CURRENT DYNAMOS. 


87 


and each transient current generated passes into the 
outer circuit through the brush which presses on one 
ring, and is returned through the brush which presses 
on the other ring, traversing the outer circuit and arma¬ 
ture coils in the direction indicated by the arrows at 
one instant, while at the next this direction is reversed, 
as already explained. 



There are two methods of connecting the armature 
coils in alternating current dynamos, known respectively 
as the series and the parallel. These are illustrated in 
Fig. 41, the series method at A, and the parallel at B. 
In the series method it will be seen that the current 
flows from coil to coil by a single wire; while in the 
parallel method the ends of each coil are joined to two 
separate wires, and the current divided between them. 
The series method gives the greatest E. M. F., or 
electric pressure, and also the greatest internal resist¬ 
ance; while in the parallel method the internal resistance 

























88 


THE ELEMENTS OF ELECTRIC LIGHTING 


is reduced, and the volume of current increased in the 
same ratio. This becomes apparent when we consider 
that since resistance in a conductor is inversely as the 
area of its cross-section, doubling the number of wires, 
if of the same size, doubles this area, halves the resist¬ 



ance, and doubles the volume of current. Hence if, in 
electric lighting, large current and small pressure are 
required, the parallel method is preferred; while if high 
pressure and small current are required, the series 
method has the preference. In both methods the alter¬ 
nate coils are wound in opposite directions for the 
reason already given, as shown in Fig. 40. 

The Wood Single Phase, Constant Potential 
Alternator. —The construction of this dynamo, as illus¬ 
trated by Fig. 42, shows an external, stationary field- 
magnet having a number of poles radiating inward from 
a circular yoke, and inclosing a rotating armature. Its 
field cores are made of laminated iron, cast into an iron 







iLTERNATING 


CURRENT DYNAMOS. 


89 






90 


TIFF ELEMENTS OF ELECTRIC TJGITTTXG . 


each other; a tine wire set traversed by a current from a 
direct current exciter dynamo, shown on the left, and a 
coarse w T ire set traversed by a current from the armature, 



Fig. 48. 


made direct by a commu- 
tator. The coils in both 
sets are wound in the same 
direction, the coarse wire 
coils over the fine wire 
coils, the winding alter¬ 
nating in direction on 
alternate poles, so as to 
produce alternate rever¬ 
sal of polarity. The wind¬ 
ing is done on a lathe 
before the coils are placed 
on the cores, and the 
proper connections made 
subsequently; and they 
are held in place by cleats 
and screws. 

The armature, shown in 
Fig. 4-3, is of the cylin¬ 
der type, and its core is 
composed of Q-shaped, 
sheet-iron rings, mounted 
on a bronze spider with¬ 
out insulating material be- 
tween them, and so placed 
that the open spaces in 
the rings shall be distrib- 
uted all through the core, so as to produce ample venti¬ 
lation. The outer edge of each ring is divided into a 
number of T-shaped teeth, which are placed in line, 





















ALTERNATING (JVRliENT DYNAMOS. 


91 


opposite each other, in the several plates, when the core 
is constructed; and the coils are wound under the flanges 
of these teeth, and secured in place by wooden wedges 
driven between them, making the armature ironclad, the 
coils being completely covered by the iron, except at the 
ends, where they are covered with bronze caps. 

The coils are composed of insulated copper ribbon, 
and are wound in two sets, those of each set being placed 
on separate, alternate teeth and connected together in 
series, and the two series connected together in parallel; 
the winding alternating in direction, as in the field coils, 
so as to produce alternate reversal of polarity. 

In Fig. 42 are shown two collecting rings on the left 
of the armature, and on the left of these, a commutator, 
all insulated from each other. The commutator is divided 
into two sections by connecting together alternate seg¬ 
ments, all the evenly numbered segments constituting 
one section, and all the oddly numbered segments the 
other section, as described on pages 109,110. There is also 
a set of German silver resistance coils, shown in Fig. 44, 
which is inclosed in the front pedestal and covered by 
the perforated screen shown in Fig. 42, which furnishes 
it with ample ventilation. These coils are connected 
with the main circuit by a shunt circuit, as shown by 
the flexible conductors terminating at the top of the 
screen, and are traversed by a small part of the main 
current. 

The two terminals of the coarse wire field-circuit are 
connected with the two commutator brushes, and the 
two terminals of the external circuit are connected with 
the two collecting ring brushes, as shown in the diagram, 
Fig. 45. One terminal of the armature circuit is con- 
nected with the right collecting ring, and the other ter- 


92 


TILE ELEMENTS OF ELECTRIO LIGHTING. 


minal with one section of the commutator, the other 
section of the commutator being connected with the left 

O 


collecting ring. 

O O 

Hence the course of the current, at a given instant, 
is from the armature to one section of the commutator, 
thence through the brush in contact with this section to 
the held circuit, where it divides, and having traversed 



Fig. 44. 


the coils on opposite sides of the field in two parallel 
currents of equal volume, and the two having united at 
a point diametrically opposite to that at which they sepa¬ 
rated, the current returns to the brush in contact with 
the other section of the commutator, and from this sec¬ 
tion it passes to the left collecting ring, and thence out 
through the external circuit, and back to the right col- 
looting ring, and thence back to the armature. 












EXCITER 


ALTERNATING CURRENT DYNAMOS. 


93 


i—'. 

qq 

pT 



RHEOSTAT 







































THE ELEMENTS OF ELECT RIO LIGHTING. 


94 


The direction of the current being reversed, the next 
wave passes out from the armature to the external circuit 
through the right collecting ring and brush, and having 
traversed this circuit in the opposite direction to that of 
the previous wave, returns to the left collecting ring and 
brush, and thence to the section of the commutator con¬ 
nected with this ring. The relative positions of the two 
commutator sections having been reversed at the same 
instant that the direction of the current was reversed, 
the current returning from the external circuit enters the 
field circuit by the same brush through which it entered 
before from the armature, and therefore traverses the 
field circuit in the same direction as before, returning 
to the armature by the other commutator brush and 
section. 

Hence it will be seen, that while the current traverses 
tlie external circuit alternately in opposite directions, it 
traverses the field circuit constantly in the same direction: 
entering it, at one alternation, direct from the armature, 
before traversing the external circuit, and, at the next 
alternation, after traversing the external circuit; always 
circulating through the coarse wire field circuit in the 
same direction as that of the exciter current which cir¬ 
culates through the fine wire field circuit. 

As the volume of current traversing the coarse wire 

field circuit in this manner varies inverselv as the resist- 

</ 

ance in the external circuit, and this resistance varies 
inversely as the work, it is evident that the excitation of 
the field by this current, and hence its E. M. F., or po¬ 
tential, is constantly kept proportional to the work done 
in the external circuit, as explained on page 111. The 
exciter current, which traverses the fine wire field circuit, 
passes through a rheostat, which is simply a set of Ger- 


ALTERNATING CURRENT DYNAMOS. 


95 


man silver resistance coils with a regulating switch; and 
by varying the resistance of this circuit in this instru¬ 
ment, the volumes of the current, and therefore the 
potential of the held due to this current, can be varied 
as required. 

The self-induction of the current, that is, the mutual 
induction on each other of adjacent convolutions of the 
coils which it traverses, both in the armature and held 
circuits, generates an abnormal degree of E. M. F., pro¬ 
ducing what is known as the extra current at the instant 
the circuit is partly interrupted at the commutator 
brushes, as they pass from one segment to another. This 
abnormal E. M. F. and current would produce a rapid 
succession of bright sparks at the brush contacts which 
would heat and injure the commutator unless suppressed; 
hence it was found necessary to introduce the shunt cir¬ 
cuit, already referred to, through which sufficient current 
is diverted from the held circuit to correct these injurious 
effects, reducing sparking at the commutator brushes to 
the minimum. This shunt current is only a small part 
of the main current, as has been stated, and can be ad¬ 
justed to its proper quantity by varying the number of 
resistance coils included in the shunt circuit. 

As the exciter is belted to the armature shaft of the 
alternator by the band-wheel on the left, as shown, the 
relative rate of speed, and therefore of electric genera¬ 
tion, must be constantly in the same proportion in the 
two machines; any variation of these in the alternator 
producing proportional variation in the exciter, the two 
being practically constituent parts of the same apparatus. 

The terminals of the external circuit are connected to 
the two binding-posts shown at the base of the front 
pedestal. 


THE ELEMENTS OF ELECTRIC LIGHTING. 


96 






ALTERNATJNG CVKRENT DYNAMOS . 


97 


The Stanley Two-Phase Alternator. —The con¬ 
struction of this dynamo is essentially different from that 
of any dynamo previously made. It is specially designed 
to supply the demand for machines which can generate 
electric current adapted both to electric lighting and the 
operation of alternating current motors, and belongs to 
that class of alternating current generators known as 
two phase, which generate two distinct series of current 
waves, or impulses, each impulse rising to its maximum 
energy while the preceding impulse falls to its minimum 
energy; thus producing an alternation in the phase of 
the current, or mental conception of the impulse as a 
wave, in addition to the alternation in its direction as 
ordinarily generated; the phase alternation specially 
adapting it to the requirements of the alternating current 
motor without interfering with its adaptation to electric 
lighting. 

By referring to Fig. 46, it will he seen that the gen¬ 
erating part of the machine is divided into two distinct 
sections, on the right and left of a central space, both 
constructed in exactly the same manner. The external, 
stationary part, in both sections, represents the armature, 
and the internal, revolving part, represents the field- 
magnet, preferably called the inductor , in this machine. 

The armature core is composed of sheet-iron laminae, 
bolted together without insulation between a pair of cast- 
iron standards, in each section; the bolts extending across 
through both sections, as shown in the central space. 
The interior surface of the core, as shown in Fig. 47, is 
divided into a number of polar projections, by grooves 
in which the coils are placed. The coils are composed 
of insulated copper wire, and are wound separately on 
forms, in rectangular shape, curved to correspond with 


THE ELEMENTS OF ELECTRIC LIGHTING 


98 





















A L TERN A TING C UR RENT I) YN 1 M OS. 


99 


the curve of the core, and are covered with insulating 
tape before being placed in the grooves, and secured in 
place by brass clamping rings. 

The armature is divided into halves, horizontally in 
the small machines, and vertically in the large ones, as 
shown in Fig. 47, for convenience in setting up and 
making repairs; and each half contains four sets of coils, 
making eight sets in all, two in each of the four sections 
produced by this subdivision. The coils in each set are 
wound alternately in opposite directions and connected 
together in series, and the sets may be connected together 
either in series or in parallel, as explained hereafter. 

Each coil incloses two core projections, as shown; one 
set being placed over the other set in each of the four 
sections, in such a manner that two opposite sides of 
each coil in the upper set rest on the centers of two adja¬ 
cent coils in the under set, as shown. The effect of this 
arrangement is to produce the two phases of the current 
already mentioned, each phase beginning at one edge of 
each coil, under the influence of the field-magnet, or 
inductor, and reaching its maximum at the center; so 
that the phase in one set of coils has reached its maxi¬ 
mum, at the instant the phase in the other set, either 
upper or under, has reached its minimum. The four 
upper sets are connected together, either in series or in 
parallel, and likewise the four under sets, but the upper 
and under sets have no electric connection whatever with 
each other. 

The field-magnet, or inductor, is shown in Fig. 48. 
It is made in two sections, identical in construction, and 
corresponding in width and position to the two sections 
of the stationary armature, within which it rotates. Each 
section consists of a set of polar projections of laminated 


100 


THE ELEMENTS OF ELECTRIC LIGHT INC. 


iron, without insulation between the laminae; all the north 
poles of one set facing all the south poles of the opposite 
set; so that the alternation of direction in the armature 
current is not produced by alternation of polarity in the 
field-magnet, but by alternation in the direction in which 
the armature coils are wound. These polar projec¬ 
tions are mounted on a circular, steel casting, supported 
on the shaft by a steel spider, and having flanged clamp¬ 
ing rings at the ends and center, between which the 
laminae are bolted. The laminae are held in place by 
flanges projecting from opposite sides of their bases, 
which fit under \/-shaped flanges on the steel casting. 
Their upper ends are made slightly convex, and the 
corners rounded, as shown, to produce smoothness in 
the phase of the current waves generated in the armature 
coils as they come within the inductive influence of the 
field-poles. 


There is only one field-coil, and it is wound on a large, 
circular, copper spool, placed in a fixed position, inclos¬ 
ing the space between the field-poles, and fitting into the 
space between the armature coils, as shown in Fig. 47. 
The current which circulates through this coil is employed 
to excite the field-magnet, and is supplied by a small, 
direct-current dynamo, or exciter, driven bv a small 
pulley, shown on the left hand of the shaft in Fig. 46; 
hence this coil is also known as the exciter coil. The 
spool is made of heavy copper to absorb and eliminate 
the static charge which accumulates in the coil when 
opening the field circuit and tends to break through the 
insulation of the wire; and this is accomplished the more 
effectually by its inclosing the coil on three sides. 

The whole machine is thoroughly ventilated, air beiim 
drawn into the interior of the field-magnet through the 


,4 L TERN. I TING CV RRENT U YNAMOti 


101 




102 


THE ELEMENTS OF ELECTRIC LIGHTING. 







ALTERNATING CURRENT DYNAMOS. 


103 


spider, and discharged by centrifugal force against the 
coils through central openings, one of which is shown in 
Fig. 48, and passes out between the field-poles. 

As there are no rotating coils in any part of this 
machine, sliding contacts constructed with brushes and 
collecting rings, as in other machines, are not required; 
the coil terminals being brought out and connected with 
each other and with the external circuits on an insulating 
terminal hoard, shown attached to the machine in Fig. 
36, and separately in Fig. 41). This hoard is constructed 
with two heavy slabs of marble, bolted together; the 
inner slab supporting twelve terminals, each of which is 
inclosed in a separate compartment by partitions on the 
outer board, when the slabs are bolted together. 

It should be carefully noticed that the two phases of 
the current are produced independently of each other, 
one phase by the under sets of armature coils and the 
other phase by the upper sets, as much so as if produced 
by two separate machines generating currents alternately 
in phase. The upper sets of coils are connected with a 
separate circuit from the under sets. Each of these cir¬ 
cuits would ordinarily have two lines of wire, four wires 
in all, parallel with each other on the same poles; but 
this is not necessary, as a single large wire may he sub- 
stituted for two of them, thus effecting a saving of about 
15$ in the amount of copper required for line wire; the 
central wire being employed to complete a circuit with 
each of the outer wires, and being 41$ larger than either 
in cross-section. A current wave, transmitted from the 
upper coils by one of the outer wires, returns to the 
dynamo by the central wire, and the next wave, trans¬ 
mitted from the under coils by the other outer wire 
returns also by the central wire; the current being 


104 


THE ELEMENTS OF ELECTRIC LIGHTING. 


reversed, the two following waves, one from the upper 
coils and the other from the under coils, pass out suc¬ 
cessively hy the central wire, each returning by the outer 
wire througli which it passed out at the previous alterna¬ 
tion. 

The lamps are connected with each of these circuits 
separately, in the same manner as on circuits from single 
phase dynamos, hut electric motors must he connected 
with both circuits jointly, so that the alternate phases of 
the current may traverse the motor in accordance with 
the special design of this dynamo. 

When the upper sets of armature coils are connected 
together in series, and also the under sets, as already 
mentioned, the E. M. F. in each circuit is double what 
it is when the connection is made in parallel; but the 
volume of current, with the parallel connection, is double 
that with the series connection. These connections are 
made on the terminal board, and are easily changed from 
series to parallel, or the reverse, as may be required; 
any connecton between the upper and under sets being 
carefully avoided. 

In making repairs, the upper half of the armature may 
he lifted, and the field-magnet removed. This can easily 
be done in the small machines, whose armatures are 
divided horizontally for this purpose; but as the weight 
of the large machines would make this method inconven¬ 
ient, their armatures are divided vertically, so that the 
two halves can he drawn apart by screws, as shown in 
Eig. 47, sliding on removable tables provided for this 
purpose, and leaving the field-magnet undisturbed. 

The construction of the self-oiling shaft hearings, with 
the loose rings for lifting the oil and distributing it on 
the bearing, according to the method now in general use, 


ALTERS A TTNG CURRENT DYNAMOS. 


105 


is fully illustrated in Fig. 50. The rings tit loosely in the 
slots shown in the hearing lining, and therefore rest on 
the shaft when it is placed within this lining, and rotate 
with it, bringing up the oil which adheres to .them, 
from the well underneath the linino*, and distributing it 
on the shaft. 



Fig. 


50. 


The Westinghouse Two-Phase, Constant Potential 
Alternator. —This dynamo, illustrated by Fig. 51, is 
similar to the Wood in appearance and in the construc¬ 
tion of its field-magnet cores and yoke, supporting base, 
and relative position of field-magnet and armature, hut 
its electric construction and coil windings are very dif¬ 
ferent. 

The yoke is made of cast-iron, in two parts, the upper 
part being removable, and the pole cores of soft steel, 
laminated, without insulation or ventilation between the 
plates, and cast into the yoke. The field-coils are wound 
on zinc bobbins, bolted to the yoke, and are so connected, 
in series, that the current traverses them alternately in 
opposite directions, producing alternate poles of opposite 
polarity. 




106 


THE ELEMENTS OF ELECTJtIO LIGHTING . 

















A L TERNA TING CURRENT I) YN I M08. 


107 


1 ho armature is of the cylinder type, and lias a lami¬ 
nated, soft steel core, without insulation between the 
plates, hut with ventilating spaces at proper intervals. 
Each plate is constructed with internal, supporting arms, 



Fig. 52. 


and external teeth, as shown in Fig. 52, and is mounted 
directly on the shaft and keyed to it; so that the entire 
core, including the arms, is laminated, and has ventilat¬ 
ing spaces between the arms, connected with those be¬ 
tween the teeth. 













108 


T1IE ELEMENTS OF ELECTRIC LIGHTING. 


The armature coils are made of thin copper bars which 
tit edgeways in slots between the teeth; each coil consist- 
ing of two bars with end terminals, properly shaped and 
covered with insulating material before being placed on 
the core. These two bars are separated by several inter¬ 
vening teeth, the slots between which are occupied by 
the bars of adjacent coils, constructed in the same man¬ 
ner. If, for instance, two bars belonging to the same 
coil occupy slots 1 and 4, the two bars of the next adja¬ 
cent coil will occupy slots 2 and 5, and those of the next 
coil, slots 3 and 6, and so on; the number of coils thus 
placed depending on the size of the dynamo, several 
bars occupying each slot. An eight pole armature, for 
instance, may have 56 coils thus placed, the two bars of 
each coil being separated by seven teeth, making eight 
sections in the entire winding; the terminals crossing 
each other at opposite ends of the core. 

When the coils are all placed on the core in this man¬ 
ner, the terminals of adjacent coils are soldered together 
in such a way as to produce a single, progressive series 
of coils all wound in the same direction; a terminal of 
coil 1, for instance, being soldered to a terminal of coil 
2, the other terminal of coil 2, to a terminal of coil 3, 
and so on; the last terminal of the last coil being sold¬ 
ered to the first terminal of the first coil; making* a 
closed circuit armature, like that of a direct current, 
closed circuit armature. The coils are then secured in 
place by strips of insulating fiber driven over them in the 
slots shown in the sides of the teeth in Fig. 52. This 
closed circuit is then tapped at four points, 90 degrees 
apart, by four wires, each of which is connected to a sep¬ 
arate collecting ring, mounted on the front end of the 
shaft; these four rings being insulated from each other 


A L TERN A TING CURRENT 1) YNA MOS. 


109 


and divided into two pairs, each pair connected with 
the armature coils at diametrically opposite points. 

The current is collected from each pair of rings by a 
pair of brushes, each pair connected with a separate, 
external, two-wire circuit; and each alternate wave, when 
generated in the coils, traverses them in two circuits, on 
opposite sides of the armature, from one tap to the oppo¬ 
site tap, where the two unite and pass out by the same 
ring and brush, returning to the opposite tap by the 
other ring and brush, after traversing the external cir¬ 


cuit. 

The effect of tapping the armature coils at four points, 
as described, is to produce two separate current waves, or 
phases, derived from the coils at distances 90 degrees 
apart, which traverse each main circuit alternately in 
opposite directions; each wave rising to its maximum 
bight while the preceding wave is falling to its minimum 
bight. The two external circuits may be constructed 
with three wires instead of four, in the manner described 
in connection with the Stanley two-phase dynamo, page 
103; in which case only three collecting rings are re¬ 
quired, two of the taps being connected to a central ring. 

The field-magnet is excited in part by a small, direct 
current dynamo, and also by a part of the current gener¬ 
ated by the armature and made direct by a commutator 
for this purpose. The latter current is generated by a pair 
of coils wound on two opposite arms of the four which 
support the armature core, and the terminals of these 
coils are extended in grooves on the shaft to the com¬ 
mutator shown near its outer end, on the right of the 
collecting rings; these coils being entirely separate from 
those which generate the main current. The segments 
of this commutator are alternately connected together in 


THE ELEMENTS OF ELECTRIC LIGHTING 


110 


two sets, all the evenly numbered segments in one set, 
and all the oddly numbered segments in another set. 

• Two pairs of brushes make contact with them at points 
diametrically opposite, and the current waves, alternat¬ 
ing in direction as the segments in each set alternate in 
relative position, all pass out in the same direction by one 
pair of brushes and return by the opposite pair and are 
led to and from the held circuit respectively by flexible 
conductors connected with it on opposite sides, at the 
base of the front pedestal. The exciter dynamo is con¬ 
nected with the held circuit in a similar manner, and its 
current traverses the held-coils in the same direction as 
the other current; the two combined constituting the 
held current. 

1 lie four wires which tap the main coils are wound in 
coils on the four arms of the armature, two of them 
beside the pair of coils described above, and are extended 
thence to the collecting rings. By this construction, 
these two sets of coils are so related to each other in 
position that the waves of current, traversing each set 
independently, are attaining their maximum strength in 
one set while declining to their minimum strength in the 
other set, as in the two main circuits. 

1 liese two sets, with the cores on which they are 
wound, constitute an apparatus practically the same as 
the transformers described at the end of this chapter. 
When a current traverses either set while there is no cur¬ 
rent traversing the other set, the self-induction generated 
between adjacent convolutions of the same coils produces 
counter E. M. F., which reduces the volume of the cur¬ 
rent; but when currents traverse both sets simultan¬ 
eously, in two phases related to each other in the manner 
described above, the self-induction in each set is neutral- 


ALTERNATING CURRENT DYNAMOS. 


111 


ized by the inductive influence of the other set, in pro¬ 
portion to the relative strength of that influence in each 
set respectively, and the volume of current traversing 
the circuit, or circuits, connected with each set is in¬ 
creased proportionally. Hence, if the main circuits are 
open and the held circuit closed, the counter E. M. F. 
due to self-induction will reduce the volume of current in 
the latter circuit to a comparatively small quantity. But 
if the main circuits are also closed for the performance 
of work, as the supplying of current to electric lamps or 
motors, the counter E. M. E. in the field circuit will he 
reduced in proportion to the volume of current travers¬ 
ing the main circuits, and hence a current of larger 
volume will traverse the field, increasing its E. M. F. 
and magnetism in proportion, approximately, to the 
work performed in the main circuits. 

This process is reversed as the work decreases, because 
less current flows through the main circuits; the resist¬ 
ance in these circuits always varying inversely as the 
number of lamps or motors taking current in parallel, 
and the volume of current varying inversely as the re¬ 
sistance. Hence the E. M. E., or potential, of the 
dynamo is constantly approximately proportional to the 
work. 

On the left end of the armature shaft is shown a 
bronze cap which covers the six terminals of the wires 
connecting with the collecting rings and commutator. 
Two of the four terminals of the external circuits are 


shown connected with two collecting ring brushes; 
also one terminal of the rectified field circuit is shown 
connected with a commutator brush; the lower end of 
this wire, when the connection is completed, extends 
down to the base of the front pedestal, and connects with 


112 


THE ELEMENTS OF ELECTRIC LIGHTING. 


the field-coils in the little block shown at the right of the 
bolt head, with which also the terminals of the exciter 
circuit are also connected as shown. 

The shaft hearings are made self-oiling by loose rings 
in the usual manner, the quantity of oil in the well being 
indicated by an oil gauge, one of which is shown on the 
front pedestal. The terminals of the main armature 
coils are confined by a band as shown, and the interior 
coils are protected by the bronze ring shown. The 
exciter is usually belted to a pulley on the engine shaft, 
but may be belted to one mounted on the armature shaft, 
outside the main pulley, if desired. 

The Converter.— A very important feature of the 
alternating current system of electric lighting, of which 
these machines form a part, is the converter, or trans¬ 
former, which may be described as an inverted induction 
coil. 

The ordinary induction coil is made with twc helices 
insulated from each other: an external helix of long, 
fine, insulated copper wire, having many turns, in¬ 
closes a helix of shorter, coarser wire, having compara¬ 
tively few turns, and this incloses a core composed of a 
bundle of iron wires. The interior helix, known as the 
primary, when connected with an electric generator 
magnetizes the core, which, by reciprocal action, in¬ 
creases the strength of the electric current ; and the 
primary circuit being opened and closed with great 
rapidity by a circuit-breaker, a series of alternate cur¬ 
rents in opposite directions is induced in the secondary 
circuit; the electromotive force of these induced cur¬ 
rents as compared with those in the primary being 
increased in the direct ratio of the increased number of 
turns. In such a coil, electromotive force is increased 


ALTERNATING CURRENT DYNAMOS. 


113 


at the expense of current strength, but in the converter, 
current strength is increased at the expense of electromo¬ 
tive force. This is effected by connecting the high resist¬ 
ance coil with the generator, and the low resistance coil 
with tl ie lamp circuit, the alternation being produced in 
the dynamo. 



Fig. 53. 


In the induction coil, the core, being in the center, is 
separated from the secondary helix by the interposition 
of the primary, and hence its magnetizing effect on the 
secondary is reduced as the square of the distance 
represented by the thickness of the primary. In the 
Westinghouse converter this arrangement is partially 




























































































































Fig. Oo. 
































AL TERN A TING CURRENT J) YNA MOS. 


115 


reversed, the two coils being placed side by side, and 
inclosed within an iron envelope which fulfills the 
magnetizing function of the core, both coils being thus 
brought into close contact with the iron. This ^close¬ 
ness of contact is effected more perfectly by dividiug 



Fiv. 56. 


the converter into connected sections having compara¬ 
tively thin coils instead of using a single large converter 
requiiing great thickness in the coils. The magnetizing 
envelope is composed of sheet-iron plates, insulated 
from each other, placed at right angles to the longer 





























116 


THE ELEMENTS OF ELECTRIC LIGHTING. 


axis of the elliptic-sliaped coils, built up around them, 
and bolted together; the proportion of iron in the 
envelope to that of copper in the coils being as 2f to 
1. The loss from electrical conversion in a reduc- 



Fig. 57. 


tion from 1,000 volts in the primary to 50 in the second¬ 
ary is said not to exceed five per cent. 

Fig. 53 gives a front view of the converter, and Fig. 
54 a view in cross-section; the fine wire at the right 
showing the primary coils, and the coarse wire at the 
left the secondary; and f f f f the magnetizing 
envelope; the edges of its plates being shown at A. 













































































































A L TEENA TING C GEE ENT 1) YNA MOS. 


117 


T he coils, composed of covered wire, and thoroughly 
insulated from each other and from the plates, are first 
wound on a form, and the plates, shaped as in Fig. 55, 
built up around them; the ends, f :i , being first bent 
back as in Fig. 55, and then laid Hat as in Fig. 54. 
The plates are then bolted together by means of the end 
frames, II x II 2 , Fig. 53, and the apparatus inclosed in 
the iron case shown in Figs. 56 and 57, by which it is 
protected from dampness, injury, and accidental contact 
with electric wires; the cases being arranged for con¬ 
venient attachment, as shown. 

Fig. 56 is a front exterior view of the case, and Fig. 
57 a sectional end view of its interior; the terminals 
and connections of the coils beiim inclosed in the com- 

O 

partments 1)^ I) 2 , fitted with glass, T T 7 , in front to 
permit inspection; the primary and secondary being 
separated from each other in each compartment by 
insulating plates, as shown at /* 2 . One terminal of the 
primary coil is shown at P above, and one of the sec¬ 
ondary coil at S below, in Fig. 57; the positions of the 
other terminals, above and below, being easily under¬ 
stood from Fig. 54. The terminals are attached to the 
bolts, f f \ mounted on the insulating plates, e t e 2 ‘ <j g , 
being safety fuses, A and i switches, and k andy 2 plugs 
for opening and closing the connections. 

In the more recent construction of transformers, the 
safety fuses are inclosed in a separate box, which is 
placed in a position easily accessible for the renewal of a 
fuse in case one melts, or u blows ” as technically termed, 
but otherwise the construction is substantially as here 
described. 

A transformer may be employed to increase the E. M. 
F. instead of reducing it as described. This is accom- 


118 


THE ELEMENTS OF ELECTRIC LIGHTING. 


plislied simply by reversing the use of the coils, employ¬ 
ing the coarse wire coil as the primary and the line wire 
coil as the secondary. When constructed in this way, 
it is known as a step-up transformer, to distinguish it 
from the usual construction, in which it is known as a 
step-down transformer. 

It is sometimes necessary either to increase or decrease 
the E. M. F. to a much greater degree than would be 
practicable by the employment of a single transformer. 
This is accomplished by employing several transformers 
connected together in series, the primary coils in one 
series and the secondary in another, as shown in Fig. 58, 
where twenty are thus connected together, each being a 
section of one large transformer. 

This requires special construction, the difference be¬ 
tween the primary and secondary coils of each section in 
the relative size of the wire and the relative number of 
turns in each coil respectively, being far less than would 
he possible in a single transformer having the same dif¬ 
ference of potential as exists between the primary and 
secondary coils at the opposite ends of this series; the 
generation of E. JVL F. being always in proportion to the 
number of turns in the coil. And the liability of the 
electric current to break through the insulation at any 
point is proportionally reduced in the series by the com¬ 
paratively low potential difference in each section. 

1 ransformers of this description are employed for long¬ 
distance transmission, where very high E. M. F. is 
required; the step-up kind being used at the end of the 
line where the electricity is generated, and the step-down 
kind at the end where it is delivered. 

Transformers designed for out-door use, mounted on 
poles and connected with the line, as shown on page 119 


ALTERNATING CURRENT DYNAMOS. 


119 





















































































120 


THE ELEMENTS OF ELECTRIC LIGHTING. 


require to be inclosed in iron eases to protect them from 
the weather. One of this kind made by the General 
Electric Co., is shown complete in Fig. 59, and its 
interior construction in Fig. 60. Its primary coil is 
inclosed within its secondary, which brings the secondary 
into close proximity with the greater proportion of the 
external iron, and more fully under the inductive influ¬ 
ence of the primary coil than when the coils are placed 
side by side. 

The secondary is divided into two separate coils of 
equal size and the same construction, placed side by side 
as shown; and these may be connected with the lamp 
circuit either in parallel or in series. When connected 
in parallel, the F. M. F. generated is only half that 
generated in the series connection, since the generation 
of E. M. F. is in proportion to the number of turns 
through which the electric current circulates in series, as 
already stated, and not in proportion to the volume of 
the current or the size of the wire in cross-section. And 
in the parallel connection, the effect is the same as if the 
wire were doubled in size, and had only half the number 
of coil turns as in the series connection; producing 
double the volume of current, but only half the F. M. F. 

These two different modes of connection are made in a 
very simple manner, on a connection board made of 
insulating material and enclosed within the cap shown 
in Fig. 59. This board is shown at A in Fig. 61, with 
the connections arranged in series, and at B, with 
the connections arranged in parallel. It has six copper 
connection plates with binding-screws attached, and is 
pierced with holes for the terminals of the coils and of 
the line circuit and lamp circuit. The two terminals of 
the primary coil, shown in Fig. 60, are brought up and 


ALTERNATING CURRENT DYNAMOS. 


121 




Fig. 61 

































































































122 


THE ELEMENTS OF ELECTRIC LIGHTING. 


attached to the plates JU and IS by two of the binding- 
screws, and the two terminals of the line circuit are 
attached to the same plates by the two remaining bind¬ 
ing-screws. The two terminals of one of the secondary 
coils shown in Fig. 60 are brought up and similarly 
attached to plates C and I), and the two terminals of the 
other secondary coil to plates E and F. One terminal of 
the lamp circuit is attached to plate E and the other to 
plate D. 

In the series connection, shown at A, the secondary 
current, entering from the lamp circuit by plate E, trav¬ 
erses the secondary coil connecting E with F, passes 
thence through the switch S 1 to plate C, traverses the 
other secondary coil connecting C with 1), and returns 
from D through the lamp circuit to E. 

In the parallel connection, shown at T>, the secondary 
current from the lamp circuit, entering as before bv E, 
divides, one half of it traversing the coil connecting E 
with F, and thence passing through the switch S 3 to 13. 
The other half passing through the switch S 3 to C, trav¬ 
erses the coil connecting C with D, and there uniting 
with the former half, returns as before through the lamp 
circuit to E. 

In both modes of connection, the line current, entering 
by N, traverses the primary coil connecting A with M, 
and returns to the line circuit from M. The direction 
of the current in both circuits and modes of connection 
has been arbitrarily assumed for convenience of descrip¬ 
tion ; hence the current may traverse the same connec¬ 
tions in reverse order. 

The supply of current to the lamp circuit at different 
degiees of E. M. I., as above described, is often found 
convenient, to adapt the current to the requirements of 


ALTERNATING CURRENT DYNAMOS . 


123 


the lamps and lamp circuits, a much higher degree of 
h«. M. 1. being required in some cases than in others. 

Ihe transformers here described belong to the step- 
down class; the usual E. M. F. of the line current 
supplied by an alternating current dynamo being com¬ 
paratively quite high, and requiring to be reduced, both 
for safety and adaptation to use, before the introduction 
of the current into a building. 

In the larger transformers of this kind, the coils are 
usually immersed in mineral oil contained in the lower 
part of the case, which is an excellent insulator; and in 
case of the other insulating material being ruptured, by 
lightning or otherwise, the oil at once flows in and sup¬ 
plies its place, thus restoring the insulation. 

Joints being always undesirable in conductors carrying 
such powerful currents as circulate through these large 
transformers, the connection boards are dispensed with, 
to lessen their number; the coil terminals being connected 
directly to the circuits, through the fuses and switches, 
at points conveniently accessible outside the case. 

The Westingiiouse Kotary Transformer. —The 
alternating current is capable of transmission to distant 
points much more economically than the direct current, 
while the direct is better adapted to certain kinds of 
work than the alternating, lienee, in the distribution of 
current from a central station, it is important to have an 
apparatus which can make the alternating current direct, 
after transmission, wherever such transformation is re¬ 
quired. This is done by the rotary transformer. 

The construction of this machine, as illustrated by 
Fig. 02, is easily understood. It consists simply of a 
direct current, compound wound, multipolar dynamo, 
whose armature coils are tapped at four points, 9<> degrees 


S?$»r M 


124 


THE ELEMENTS OF ELECTRIC LIGHTING 



■ S-, 


Fig. 62. 












ALTERNATING CURULJNT DYNAMOS- 


125 


apart, by wires connected with the four collecting rings 
shown on the left end of the armature shaft. The 
current is received from a two-phase alternator by four 
brushes in contact with these rings, and after traversing 
the machine and being made direct by the commutator 
shown on the right, is transmitted by the commutator 
brushes through the external circuit. The rotation of 
the armature is produced by the current, as in the elec¬ 
tric motor; hence the machine is appropriately called a 
rotary transformer , since it has the functions of self 
rotation and current transformation. 

It should be stated here, that the construction of an 
electric motor is practically the same as that of a dynamo, 
so that a dynamo can be used as a motor, as in this case; 


the armature of a dynamo being rotated by an external 
force in opposition to the magnetism generated by its 
own current, while the armature of a motor is rotated in 
obedience to the magnetism generated by a current 
derived from an external source, as a dynamo or battery. 

A small, two-pliase, alternating current motor, not 
shown, is employed to start the transformer, and after 
proper speed has been attained, this motor is stopped by 
opening its circuit, and the transformer being put in 
operation by closing the main circuit, this rate of speed 
is maintained. 

Relative Importance of Alternating Current Dy¬ 
namos.— The great improvements made in the construc¬ 
tion of these dynamos within the last ten years has 
brought them into relatively greater importance than 
formerly, as compared with direct current dynamos. 
T1 lese improvements have overcome the defects which 
earlier restricted their use, without interference with the 
primary advantage, which they always possessed, <>1 the 


THE ELEMENTS OF ELECTRIC LIGHTING. 


120 


elimination of tlie costly commutator, with its resistance, 
and the consequent greater E. M. F. which they are 
capable of generating, by which the electric current can 
he transmitted to relatively greater distances by smaller 
wires, thus effecting greater economy in line construction. 

I he construction of practical, alternating current mo¬ 
tors, which were almost unknown ten years ago, has also 
contributed materially to this result; so that the alterna¬ 
ting current can now be employed for the transmission 
of power, as well as for electric lighting, and applied 
without rotary transformation to the operation of ma¬ 
chinery by these motors; while the construction of the 
rotary transformer renders its application to direct cur¬ 
rent motors, after transformation, also possible. 


CHAPTER V 


Electric Terms an i> Onits. 

Before entering upon an investigation of the prin¬ 
ciples which govern the construction of electric lamps, 
it is proper to define more fully various technical terms 
in common use in electric science, most of which have 
been frequently used in the preceding chapters, accom¬ 
panied, as introduced, by brief definitions. This is the 
more important since their full import is not always 
clear, even to many who daily use them. 

Electric Potential. — Potential is a convenient 
term used in various departments of physical science 
to represent the energy which a body may possess to 
accomplish work. A weight has gravity potential when 
it occupies such a position that it can accomplish work 
by its descent, a furnace, heat potential when it can 
accomplish work by its heat. So practically, without 
reference to mere theoretical distinctions, electric po¬ 
tential is the power which a body possesses to ac¬ 
complish work by virtue of its electricity. But to 
accomplish work by gravity, heat, electricity, or other 
energy, there must always be a difference of potential, 
since in equality of potential the forces are equally 
balanced: a weight requires difference of level, heat, 
difference of temperature. So electricity can accom¬ 
plish no work where the opposing electric conditions 
are equal; and the object of any electric generator, 


128 


THE ELEMENTS OF ELECTRIC LIGHTING. 


whether it be a battery, dynamo, or static machine, is 
not to create electric energy, — which is a physical impos¬ 
sibility, since, like gravity, it exists as a universal prop¬ 
erty of matter, — but to create a difference of electric 
potential. 

Positive and negative are convenient relative terms 
to express differences of potential. A body is said to 
be positively electrified when by electric accumulation 
its potential rises above that of other bodies to which 
it may be related, either by contiguity of position or 
electric connection ; and negatively when its electric 
potential is below that of the other bodies. 

Electro-motive Force. — Electro-motive force is 
the force or pressure which electric energy is capable 
of exerting by virtue of a difference of electric potential 
between the body in which it is accumulated and some 
other body. The force or pressure is exerted by the 
energy itself, the body in which it is accumulated or by 
which it is transmitted being merely a passive medium, 
and not, as in the case of steam and some other bodies, 
the active medium by which the energy is applied. 

The term pressure has recently come into use in this 
connection, and perhaps expresses more clearly what 
takes place than any other term which can be found. 
It is the energy accumulated in steam, heated air, a 
descending weight, or a waterfall, which creates the 
pressure by which work is accomplished; and similarly, 
by its own peculiar process, electricity creates pressure, 
and accomplishes work. 

The symbol for electro-motive force is E. M. F., and 
in mathematical formulae E alone is generally used. 

Resistance. — Resistance is that which opposes elec¬ 
tro-motive force; it may consist in counter electro-motive 


ELECTRIC TERMS AND UNITS. 


129 


force, in useful work to be accomplished, in the imper¬ 
fect conductivity of the conductor, or in an artificial 
obstruction placed in the circuit for a given purpose. 
It is important to distinguish carefully between internal 
resistance, which pertains to the generator or any electric 
instrument, and external resistance, which pertains to the 
general circuit. R is the symbol of resistance; and where 
both kinds are referred to in the same connection, r is used 
to indicate the internal, and R the external, resistance. 

Current. — Current is that electric condition in a 
conductor which results from electro-motive force modi¬ 
fied by resistance. It pertains exclusively to what is 
understood as electric movement, and is used in the 
same sense when applied to this movement in a con¬ 
ductor, as when applied to the flow of water in a pipe ; 
and in this sense also are used the terms current inten¬ 
sity, quantity, volume, strength, and resistance ; and on 
this principle all the various kinds of electric apparatus 
pertaining to current are constructed, and current esti¬ 
mates and measurements made. In the present imper¬ 
fect state of electric knowledge, this is doubtless the 
best that can be done; and yet it is doubtful whether 
there is any real resemblance between an electric current 
and a liquid current, or current of vapor or air. The 
generator creates E. M. F. at one end of the conductor, 
and a molecular movement is supposed to take place by 
which electric energy is instantly transmitted. Theo¬ 
retically, this molecular movement is in the form of 
transverse vibrations; but as a matter of fact, its nature 
is unknown. It seems to be well established, however, 
that there is no transmission of any thing in the nature 
of a fluid or other matter, energy alone being trans¬ 
mitted, using matter as its medium. 


130 


THE ELEMENTS OF ELECTRIC LIGHTING. 


Current movement is always from higher to lower 
potential, or, which is the same thing, from positive to 
negative. Hence, since E. M. F. depends on difference 
of potential, the strength of current passing through a 
circuit of no resistance from the positive to the nega¬ 
tive side of the dynamo depends solely on the amount 
of this difference. But when the circuit includes lamps 
or other resistance, the strength of current depends on 
the E. M. F. divided by the resistance, according to 
Ohm's law, the case being analogous to that of water 
flowing through a pipe under pressure and resistance. 
Hence any variation, either of E. M. F. or resistance, 
changes the strength of the current; and where current 
constancy is required, as in electric lighting, it can be 
obtained by varying the E. M. F. in the same ratio as the 
resistance; and this, as we have seen, is done, in most 
cases, by shifting the position of the brushes on the 
commutator, in others by varying the number of arma¬ 
ture or field-magnet coils in circuit. The strength of the 
current can also be varied by varying the resistance 
of a weaker opposing current, as has been shown. 

To the ordinary mechanic or business man, accus¬ 
tomed to deal with material forces, and unversed in 
philosophic subtleties, the movement of electric energy 
in a conductor is often a profound mystery. He natur¬ 
ally associates energy and matter so intimately that he 
is unable to discriminate between them, or to conceive 
how energy can traverse a conductor unless it is a ma¬ 
terial substance of the nature of a fluid. And until 
recently philosophers found the same difficulty; hence 
the terms phlogiston and electric fluid, representing 
imaginary material substances, the supposed active 
principles of heat and electricity. 


ELECTRIC TERMS AND UNITS, 


131 


But while we do not know just how electric energy 
is transmitted, it is not difficult to conceive how it may 
be, since we have analogous instances; and the theory 
most generally adopted is that of vibration, which is 
the more probable since it is equally applicable to the 
kindred forms of energy, light, and heat. According 
to this theory, the molecules of the conductor are 
thrown into a state of intense vibration, transverse 
vibrations traversing it, and transmitting the energy 
in a manner analogous to that by which mechanical 
energy is transmitted through a series of suspended 
balls, or along the surface of a liquid. 

The symbol of current is C ; and the conductivity of 
a conductor, that is, its current capacity, without refer¬ 
ence to the material of which it is composed, is 
inversely as its length, and directly as the area of its 
cross-section. 

Electric Induction. — By electric induction is 
meant the influence which a charged conductor exerts 
on another conductor in its vicinity, insulated from it. 
It may be considered under two divisions, — static 
induction and current induction; static induction per¬ 
taining to accumulators, as Leyden jars and condens¬ 
ers ; and current induction pertaining to the mutual 
influence of currents. 

If an accumulator is charged positively, it produces 
a corresponding negative charge on all bodies in its 
immediate vicinity, electricity equal to that of the pos¬ 
itive charge being repelled from them: if negatively 
charged, a correspondingly equal positive charge is 
attracted, and accumulated on them. In either case 
there is no electric transfer of such a nature as to 
reduce the original charge: the accumulator, if posi- 


132 


THE ELEMENTS OF ELECTRIC LIGHTING 


tively charged, loses no electricity; and, if negatively 
charged, it gains none. This is proved by the fact, 
that, where surrounding objects are subsequently re¬ 
moved beyond the influence of the charged body, no 
permanent effects remain on them unless special means 
are used to render such effects permanent. This may 
be demonstrated by placing a gold leaf electroscope in 
the vicinity of the charged body, when the leaves will 
indicate the charge by their divergence; but on being- 
removed, they converge again. To make this effect 
permanent, let the plate of the electroscope, while under 
the influence of the charge, be touched by a conductor 
connected with the earth; a transfer of electricity will 
now take place, either to or from the earth, according 
as the charge is positive or negative, establishing equi¬ 
librium between the electroscope and charged body, as 
indicated by the convergence of the leaves, thus proving 
the fact of attraction or repulsion of electricity, as 
stated above; then, on the removal of the electroscope 
from the influence of the charged body, difference of 
potential asserts itself, and the leaves diverge. Now, 
since the electroscope is simply one of the surrounding 
bodies under inductive influence, so constructed as to 
indicate it, we must infer that all other bodies similarly 
placed are similarly influenced. 

Induction can take place only through an insulating 
medium, — as air, glass, or an insulating envelope,— 
which is termed the dielectric. Its nature is not fully 
understood ; but since there is no actual transfer of elec¬ 
tricity, and since energy can act only through matter 
as its medium, it is evident that the dielectric, in some 
unknown manner, becomes the medium of this subtile 
influence. The definition, “direct action at a dis- 


ELECTRIC TERMS AND UNITS. 


133 


tance,’ formerly used by some leading electricians, is 
too vague, and has been abandoned since the nature of 
electric action has come to be better understood. 

Current induction is of the same nature as static, 
modified by the properties peculiar to currents. That 
which we call a continuous current is in reality a succes¬ 
sion of impulses or infinitesimal currents, as has been 
already explained; and the conductor throughout its 
entire length, whether it be an Atlantic cable or a foot 
of wire, has practically, at each successive instant, a 
static charge modified by the difference of potential 
between its extremities, by virtue of which the trans¬ 
fer of energy takes place ; consequently this charged 
conductor, like other charged conductors, exerts induc¬ 
tive influence on adjacent conductors. 

When a current flows through a conductor, it is 
found that the effect of induction is to produce an 
opposite current in any adjacent parallel conductor. 
The nature of this action may be represented by the 
following diagram : 

00 + 10 —|—1 —{—|—\- -\ —I—hi 
2 -i 

Let a represent a conductor in which a current is 
flowing from left to right by virtue of the difference of 
potential represented by -j- 10 at the left and -f- 1 at 
the right; and let b represent an adjacent parallel con¬ 
ductor. Since inductive influence radiates from the 
charged body equally in all directions, only a small 
fraction of the lines of electric force radiating from a 
are intercepted by b; but, for convenience, we may 
represent this fraction by — J at the right, and — 2 at 
the left. Now, since, as has been shown, the positive 



134 


THE ELEMENTS OF ELECTRIC LIGHTING. 


produces by induction an equal corresponding negative, 
and vice versa , the positive potential in a, represented by 
+ 10, produces, under the conditions named, a negative 
potential in £>, represented at the adjacent point at the 
left by — 2, while at the right -f- 1 in a produces — 
in b ; and since electric movement is always from higher 
to lower potential, the current in b must flow from right 
to left, opposite to that in a. 

Hence, when currents in two or more adjacent paral¬ 
lel conductors flow in the same direction, the effect of 
their mutual induction is to produce in each a counter- 
current, which reduces the volume of the primary cur¬ 
rent ; the effective current by which useful work is 
accomplished being then represented by the difference 
between the two. As in the illustration, if the primary 
current were represented by 10, and the induced op¬ 
posing current by 2, the effective current would be 
represented by 8. 

But if the primary currents flow in opposite direc¬ 
tions, the effect of induction is reversed, and the volume 
of effective current in each conductor increased, as can 
easily be seen by the following diagram: 

(c) + 10 -f- + + H—h + + + + 1 

00 + 1 + + + + + + + + + 10 

in which the current in c flows from left to right, and 
in d from right to left. The positive potential 10, at 
the left of <?, induces at the same end of d a much 

stronger negative than the potential 1, of d , can induce 

in <?: consequently the difference of potential between 
the opposite extremities of d must be greater than if c 
were removed, and hence its E. M. F. and resulting vol¬ 
ume of current must be greater. And the same effect 


ELECTJUC TERMS AND UNITS. 


135 


in c must follow from the difference of potential at the 
right between the 10 of d and the 1 of c. 

The effect of induction in increasing current strength 
at the expense of E. M. F., or E. M. F. at the expense of 
current strength, has already been sufficiently explained 
in connection with the subject of converters, treated of 
in Chapter III., so that further reference to it is un¬ 
necessary. 

Magnetic Induction. — Magnetic induction, while 
strongly resembling electric induction, must be carefully 
distinguished from it: their effects are reciprocal, not 
identical. Practically, magnetic induction is found only 
in connection with iron and steel, though some other 
metals are slightly magnetic; and, as we have seen, the 
construction and operation of the dynamo is dependent 
on the reciprocal action of magnetic and electric induc¬ 
tion, the electric current being generated by the mag¬ 
netic induction of the iron cores of the field-magnets 
and armature, and reciprocally, magnetism being gene¬ 
rated by the electric induction of the current in the 
coils. The directions of the magnetic and electric cur¬ 
rents produced by this reciprocal induction are always 
at right angles to each other; the magnet and the coil 
or line conveying the electric current, if free to move, 
always assuming this relative position with respect to 
each other. 

The induced current, as has been repeatedly stated, 
is a momentary transient impulse which occurs at the 
instant an electric circuit is either opened or closed ; 
its direction on the opening of the circuit being the 
reverse of that on the closing: and the continuous cur¬ 
rent of the dynamo, whether constant or alternating, is 
composed of a series of these impulses, induced, not by 


THE ELEMENTS OF ELECTRIC LIGHTING. 


136 


the opening or closing of the circuit, but by a reversal 
of the position of the coils of the armature by their 
rotation, and consequently of the relative direction of 
magnetic induction. 

In the case of induction coils, the primary circuit is 
opened and closed successively, with great rapidity, by 
a circuit-breaker, and the series of impulses constituting 
the current, in the secondary circuit induced thereby. 
It is found that the current induced by the opening of 
a circuit is far more powerful than that induced by the 
closing. This is due to the transient current termed 
extra , resulting from self-induction between the adjacent 
windings of the coil; which is inverse on closing the 
circuit, neutralizing the original current to the extent of 
its strength, but direct on opening, adding its strength to 
that of the original current. The greater strength of the 
latter current, in the primary coil, is shown by the spark 
which appears at the break, on opening the circuit, 
but is never seen on closing it. In the case of acci¬ 
dents requiring the sudden stoppage of the dynamo, it 
is of the highest importance that the greater energy of 
this current should be guarded against by suitable con¬ 
struction, such as a short-circuiting switch or other 
similar device. 

In concluding these remarks on the nature and gen¬ 
eral principles of induction, which have been thus 
briefly indicated, it should be stated that when we 
consider that induction permeates every portion of 
every electric instrument, its force radiating from 
every charged conductor, the great importance of a 
thorough comprehension of its principles and their 
application becomes evident. It must be recognized, 
not as an obstacle to be overcome, — though it often 


ELECTRIC TERMS AND UNITS. 


137 


stands in the way of desirable ends in construction,— 
but as an important factor in the accomplishment of 
electric work, without which the construction and 


operation of the existing forms of electric apparatus 
would be an impossibility; and it is coming to be 
understood that it is better always to recognize it as 
a friend than as a foe. 

Conductivity and Insulation. — Conductivity is 
that quality of a body which facilitates electric trans¬ 
mission : insulation is its opposite, and obstructs electric 
transmission. The distinction between the two when 
applied to bodies is one of degree, the one being the 
reciprocal of the other. There is no well-defined bound¬ 
ary showing where conductivity ceases, and insulation 
begins; every conductor is an insulator so far as it 
tends to resist electric transmission, and every insulator 
is a conductor so far as it tends to facilitate such trans¬ 
mission. Where conductivity is found to predominate, 
as in the metals, the term conductor is applied; and 
where insulation predominates, as in glass and vulcanite, 
the term insulator is applied. The terms high and low 
are applied to conductors to designate different degrees 
of conductivity, or, conversely, different degrees of 
resistance ; and to insulators to designate different 
degrees of insulation. Silver and copper, for instance, 
are metals of the highest conductivity, and conversely 
of the lowest resistance: bismuth and german-silver 
have high resistance, and consequently low conduc¬ 
tivity. Glass and vulcanite have high insulation, and 
correspondingly low conductivity, — so low that the 
term conductor is never applied to them ; nor is the 
term insulator ever applied to silver or copper. Hence 
a conductor is any substance of such low resistance that 


138 


THE ELEMENTS OF ELECTRIC LIGHTING. 


it can be used practically for the transmission of elec¬ 
tricity, and a non-conductor or insulator is any substance 
of such high resistance that it can be used practically to 
prevent such transmission. 

Difference of molecular constitution is the most 
reasonable explanation that can be given of these 
different phenomena; but just how such difference pro¬ 
duces these varied results, is unknown. But we may 
reasonably attribute them to difference in molecular 
arrangement. If we compare the molecules to an 
infinite number of infinitesimal tubes, and electricity 
to a fluid passing through them, it is evident that were 
these tubes placed end to end, in series, the flow would 
be facilitated; but if disposed traversely, or in a hetero¬ 
geneous manner, the flow would be obstructed. Simi¬ 
larly we may suppose the relative arrangement of the 
molecules in one substance to be such as to facilitate, 
and in another to obstruct, electric transmission. If, as 
seems highly probable, electricity is a mode of molecu¬ 
lar motion by which energy manifests itself, the above 
explanation seems entirely reasonable; difference of 
arrangement or difference of shape in the molecules, or 
both combined, producing differences in the mode of 
interaction. 

Quantity and Intensity. — The comparatively 
imperfect state of electric knowledge has led to a 
misuse of the terms quantity, intensity, and strength 
as applied to current, each writer using them according 
to his own mental conception of the facts, or carelessly 
following the general custom. Whatever current may 
be, its quantity, as observation proves, must be re¬ 
garded in the same light as that of any physical quan¬ 
tity ; so that whether we consider it as energy flowing 


ELECTRIC TERMS AND UNITS. 


139 


through the conductor as its passive medium, or as 
producing molecular motion in the conductor itself, 
as already explained, it has a certain volume in the 
same sense as a fluid — water or gas — flowing through 
a pipe; and this volume, as in the case of fluids, is 
dependent on the resistance encountered and the press¬ 
ure urging it forward, known as E. M. F. With a 
given conductivity and E. M. F., any increase of cross- 
section by the substitution of a larger conductor, or a 
greater number of conductors, produces an increase in 
the quantity or volume of the current, and a corre¬ 
sponding decrease of intensity at each point in cross- 
section, by distributing the original intensity over a 
larger area; and a reversal of these conditions produces 
the opposite effect. Conversely with a given conduc¬ 
tivity and cross-section in the conductor, any variation 
in the E. M. F. produces a corresponding variation of 
intensity. 

Electric intensity has been regarded as analogous to 
momentum; but since momentum is the product of 
mass and velocity, and since mass is not a factor in 
electric intensity, the analogy fails. But if we regard 
electric intensity as the result of molecular movement 
in the conductor, produced by E. M. F., we shall 
probably come nearer the exact truth. 

It has also been assumed that the constancy of an 
electric current is maintained by an increase of velocity 
in the inverse ratio of the reduction of cross-section in 
the conductor, in a manner analogous to that in which 
constancy of quantity is maintained in a fluid current 
by an increase of velocity in the inverse ratio of reduc¬ 
tion in size of pipe, the same quantity passing through 
the smaller pipe in the same time as through the larger, 


140 THE ELEMENTS OF ELECTRIC LIGHTING. 


by an increase of velocity; but since the velocity of an 
electric current has never been estimated except by 
the remotest approximation, the analogy fails, as in the 
former instance. But if we regard varied quantity and 
intensity of molecular vibration, produced by a variation 
in the amplitude or the length of the waves, by which 
electric energy is supposed to be transmitted, as the 
true explanation, our conceptions of these phenomena 
become much clearer. 

Electric Units. — In order to render possible the 
calculations' required in the various departments of 
electric work, and especially in electric engineering, 
it becomes necessary to have certain units of measure¬ 
ment especially adapted to the peculiar electric condi¬ 
tions found in electro-motive force, resistance, and 
current. It is also necessarv that these units should 
be established by some authoritative source, universally 
recognized and acknowledged. The International Elec¬ 
tric Congress, composed of leading electricians of vari¬ 
ous nationalities, which met at Paris in 1881 and 1884, 
was such a body; and the electric units it adopted after 
careful deliberation have been accepted as authorita¬ 
tive. Most of these units were previously in use; and 
the work of the Congress consisted chiefly in giving 
them definite value, referable to fixed standards, and 
eliminating various errors. 

The work accomplished by electric energy furnishes 
the means for absolute measurement, and the C. G. S. 
mechanical unit is taken as the basis for the electric 
unit. I he initial letters, C. G. S., are the symbols of 
the three factors, space, mass, and time; C. standing 
for centimeter, G. for gramme, and S. for second. 
Hence this 0. G. S. unit represents the work accom- 


ELECTRIC TERMS AND UNITS. 


141 


plishecl by the movement of a mass equal to one 
gramme through a space equal to one centimeter in 
one second, known as the erg. 

The term “legal" is applied to the units adopted by 
the Paris congress to show that they are properly 
authorized, and to distinguish them from similar units 
previously in use. Hence, the following are the practi¬ 
cal legal electric units based on the C, G. S. system : — 

The Volt. — The unit of electro-motive force is the 
volt, named after Volta, the original inventor of the pri¬ 
mary battery. The E. M. F. of a battery cell nearly 
equal to that of the Daniell, was originally adopted as the 
standard unit; but, as the E. M. F. of a cell represents 
a variable quantity, a definite value was given this unit 
by the adoption of 100,000,000 C. G. S. units as the 
standard, which consequently represent the amount of 
electric energy, which, if converted without loss, would 
equal this amount of mechanical force; but, as large 
numbers are inconvenient to write, the equivalent ex¬ 
pression, 10 8 , has been adopted, and the same method of 
notation followed in regard to the other units. Hence, 
the legal volt equals 10 8 C. G. S. units. In approximate 
calculations, where strict accuracy is not required, the 
E. M. F. of the ordinary Daniell cell is still taken to 
represent the volt, its energy being about 1.05 volts. 

The Ohm. — The unit of resistance is the ohm, 
named after Ohm, who discovered and formulated the 
law of electric resistance. The resistance of a mven 

o 

number of feet of wire — copper, iron, or german-silver 
— of a given gauge was the original standard; but the 
Paris congress, acting upon the suggestion of Sir 
William Siemens, adopted as the standard a column of 
pure mercury, 106 centimeters m length, and 1 square 


THE ELEMENTS OF ELECTRIC LIGHTING. 


1 42 


millimeter in cross-section, at the temperature of 0° C. 
Its resistance is represented, to within a small fraction, 
by 10 9 C. G. S. units; the actual resistance represented 
by this expression being equal to that of a column of 
mercury, of the same section and temperature, 106.21 
centimeters in length; but, to avoid the fraction, the 
standard was fixed as above. The legal ohm, then, 
equals 10 9 C. G. S. units of resistance. 

The Ampere. — The unit of current strength or 
volume, as has been explained, is the ampere, named 
after Ampere, who discovered and formulated the laws 
of electric currents. It is derived from the two pre¬ 
ceding units in accordance with Ohm’s law; current 
being equal to E. M. F. divided by resistance 



lienee since 


10 8 

10 9 



— —, the legal ampere 


equals 10 _1 C. G. S. units of current strength. The 
element of time is not included in this unit. It refers 
exclusively to the strength of the current, as represented 

by its cross-section. 

The Ampere-Hour. — The ampere-hour is a unit 
derived from the last, in which the element of time is 
included. It represents a current of one ampere flow¬ 
ing through a conductor for one hour, or its equivalent 
in a greater or less current for a greater or less time, 
as two amperes for half an hour, or half an ampere for 
two hours. It is of recent origin, but is sanctioned 
by general use, and is often convenient in electric 
calculations. 

The Coulomb. — The unit of current quantity, con¬ 
sidered with reference to time, is the coulomb, named 
after Coulomb, to whom is due the first attempt at 



ELECTRIC TERMS AND UNITS. 


143 


accuracy in electric science. It is derived from the 
ampere, and represents the quantity of electricity which 
flows in a current of one ampere in one second. 
Hence, any variation, either in the time or strength 
of current, produces a corresponding variation in the 
quantity represented in coulombs; a ten-ampere cur¬ 
rent flowing for one second, or a one-ampere current 
flowing for ten seconds, represents ten coulombs ; and, 
since there are 3,600 seconds in an hour, 3,600 coulombs 
equal one ampere-hour. The coulomb equals 10 _1 
C. G. S. units of current quantity. 

The Farad. — The electric unit of capacity is the 
farad, named after Faraday. It represents the storage 
of one coulomb of electricity in a condenser; and, when 
such storage raises the potential to one volt, the con¬ 
denser is said to be of one farad capacity. The farad 
equals 10 ~ 9 C. G. S. units of capacity. 

The Microfarad. — The farad being inconveniently 
large for practical use in the construction of condensers, 
the microfarad, representing one-millionth of a farad, 
has been adopted in its stead. Hence the microfarad 
equals 10 ~ lo C. G. S. units of capacity. 

The Watt. — The unit of electric power is the watt, 
named after Watt the inventor of the steam-engine. It 
is derived from electro-motive force and current com¬ 
bined, neither of which, taken alone, is an exact repre¬ 
sentative of electric power, since current is derived 
from resistance and E. M. F., either of which may vary, 
producing a variation of current; or one may vary 
directly as the other, producing a constanc}^ of cur¬ 
rent ; hence, to obtain an accurate expression for elec¬ 
tric power, or rate of work, the E. M. F. is multiplied 
into the current, — that is, the volt into the ampere. A 


144 


THE ELEMENTS 


OF ELECTRIC LIGHTING. 


watt then equals one volt multiplied into one ampere, 
which equals 10' C. G. S. units of power (10 8 xio->^ 
10'). The term volt-ampere is synonymous with watt. 

The Electric House-Power. — The electric horse¬ 
power, which is the equivalent of the mechanical horse¬ 
power, is represented by 746 watts, equal to 746 X 10' 
= 7,460,000,000 C. G. S. units of power. 

The Jotjle. — The electric unit of heat is the joule, 
named after Joule who discovered and formulated the 


nuv by which the electric current develops heat. It 
represents the heat developed in a conductor by one 
watt in one second; which equals the square of the cur¬ 
rent’s strength multiplied by the resistance and time, 
represented by 11 — C'Rt ; 11 representing heat and t 
time; which, reduced to the C. G. S. units represented 
by (1 amp.) 2 X 1 ohm X 1 sec., gives II — X 10 9 X 1 
= 10 , 000 , 000 . 


Joule found that the heat required to raise the tem¬ 
perature of 1 gramme of water 1° C. is equivalent in 
work to 42,000,000 C. G. S. units, which is known as 

Joule’s equivalent. 

As the ratio of the joule to this is gSS = 0.238, this 
fraction represents the relative amount of heat which the 
joule can develop. Hence the formula, C l Rt , must he 
multiplied by 0.238 to reduce the C. G. S. units of work 
represented by the joule to heat units, as represented by 
Joule’s equivalent, which gives U — (J 2 Rt x 0.238, 

The Henry. —The unit of inductance (or self-induc¬ 
tion) is the henry, named after Henry, the first observer 
of this principle. It represents the induction in an elec¬ 
tric circuit, when the induced E. M. F. is 1 volt, and 
the inducing current varies at the rate of 1 ampere per 
second. Its value is 10 ,J C. G. S. units. 



CHAPTER VI. 


Electric Measurement. 

Instruments for electric measurement are con¬ 
structed either on the principle of electric attraction 
and repulsion, on the relations between electricity and 
magnetism and between resistance and E. M. F., on the 
heat developed by the electric current, or on the amount of 
metal deposited or gas generated by electrolysis. Those 
constructed on the principle discovered by Oersted, that 
the magnetic needle tends to assume a position at right ' 
angles to the direction of the electric current, are known 
as galvanometers, and are chiefly used to measure bat¬ 
tery currents; while those constructed on the principles 
of electrolysis are known as voltameters, and are used 
to measure the electro-motive force of batteries. But 
the powerful currents and great E. M. F. developed by 
the dvnamo, has led to the invention of instruments 
of special construction, known chiefly as voltmeters and 
ammeters ; voltmeters designating those which measure 
electro-motive force, the results being given in volts ; 
and ammeters those which measure current strength, 
the results being given in amperes. Ammeters are also 
called current meters and ampere meters. There are 
also instruments of special construction designated as 
electro-dynamometers, coulomb-meters and ohm-meters. 

It is evident, that since current is derived from E. 
M. F. and resistance, if two of these three quantities 


146 


THE ELEMENTS OF ELECTRIC LIGHTING. 


are known, the third can easily be found by one of the 
following formulae, 



(E = CR), 






Hence 0 and E being ascertained by measurement, R can 
be ascertained by calculation. 

There are also instruments known as potential 
indicators, which do not measure E. M. F., but are 
arranged to indicate deviations above or below a certain 
normal E. M. F., and are placed permanently in the 
circuit, like the steam-gauge on the boiler, as a guide to 
the engineer or attendant; while measuring instruments 
are used chiefly in making tests. 

The Potential Indicator. — Fig. 63 shows a 
potential indicator used by the United States Electric 
Lighting Company. It is constructed on the principle 
of the electric motor, or reversed dynamo, current pro¬ 
ducing motion, instead of motion producing current. 
Two horse-shoe magnets with consequent poles, placed 
horizontally, as shown, form the magnetic field in 
which is placed the armature, shown at the center; 
the armature core is a cylinder of soft iron, lami¬ 
nated, placed vertically in a fixed position. A helix 
of fine copper wire, wound on a copper ring and placed 
vertically also, surrounds the core, but is insulated from 
it, an air space intervening between them. This helix 
is suspended by a fine phosphor-bronze wire attached 
below to the base of the instrument, and above to a 
screw with a milled head, connected to a short arm 
projecting from a vertical support. A long pointer pro¬ 
jects towards the front, and is bent downwards at right 
angles over a circular scale, which indicates, to the nVht 

7 P > 


ELECTRIC MEASUREMENT . 147 

fh e volts above, and to the left, five volts below, a certain 
normal E. M. F. indicated by zero ; each of the numbers, 
10, 20, 30, 40, 50, indicating about a volt, and each volt 
space being subdivided into tenths, as shown. The in- 



Fig. 63. 

strument is inclosed in a glass case, and supported on 
leveling screws. It has a very high resistance, and is 
connected directly between the positive and negative 
leads at the point where the electric pressure should be 



















































































148 THE ELEMENTS OF ELECTRIC LIGHTING. 

kept constant. The resistance being very high, only a 
very small fraction of the current will pass through it. 
The armature helix is connected in series with the field- 
magnet coils, as in the series dynamo ; and the cur¬ 
rent causes it to rotate round its core so as to move 
the pointer over the scale from left to right in op¬ 
position to the torsion of the wire by which it is 
suspended, current producing motion as stated above. The 
torsion is so adjusted that the required E. M. F. brings 
the pointer to zero ; hence its movement to the right of 
zero shows that the E. M. F. is too high, or, to the left, 
that it is too low. By an increase or decrease of torsion, 
the normal E. M. F. can be varied within certain limits. 

Voltmeters and Ammeters. —The difference between 
these two instruments consists chiefly in the respective 
resistance of each, and its relative position in use; the 
voltmeter having high resistance and being placed in a 
derived circuit between the points whose difference of 
potential is to be measured, while the ammeter has low 
resistance and is placed directly in the main circuit at 
any point where current strength is to be measured. 

The Weston Voltmeter. —This instrument, shown by 
Fig. 64, incloses within its case a powerful steel horse¬ 
shoe magnet, the poles of which project into the narrow 
space in front and are attached to two soft-iron pole- 
pieces, as shown in Fig. 65. These inclose a circular 
space, within which is mounted a soft-iron armature 
core, maintained in a fixed central position by attach¬ 
ment to a brass yoke which connects the pole-pieces; 
part of this yoke, with its right-hand connection and a 
central projection for attachment of the core, being 
shown. 

A light copper frame, f of an inch wide, and wound 


ELECTRIC MEASUREMENT. 


149 

with a coil of line, insulated, copper wire, surrounds the 
core, and has a limited rotary motion, on jewelled hear¬ 
ings, in the narrow space between the core and pole- 
pieces, which is just wide enough to allow rotation with* 
out contact. 

The terminals of the coil are connected above and 
below with two flat springs, oppositely coiled, and so 
attached to the copper frame and adjoining parts as to 
maintain the coil in a fixed position, when the springs are 
not under tension, and bring a light aluminium pointer, 
attached to the frame, to zero of the scale on the left. 



Fig. 64 . 

These springs are made of a special, non-magnetie 
alloy, and are placed in opposition to neutralize the 
effects of expansion and contraction under variations of 
temperature. 

A resistance coil, mounted within the case, makes 
electric connection, by one of its terminals, with one of 
the springs, while the other terminal is connected with 
the front binding-post on the left. Another connection 
with the rear binding-post on the same side taps this coil 
at a point nearer the spring, so as to include a much 








150 THE ELEMENTS OF ELECTRIC LIGHTING. 

lower resistance. The other spring is connected with 
the binding-post on the right, back of which is a contact 
key and a calibrating coil. This part of the circuit can 
be closed permanently, after calibration, by depressing 
the key and giving it a quarter-turn. 

When connections with an electric source are made by 



Fig. 65. 


the right binding-post and either of the two on the left, 
the current enters and leaves the copper coil through 
the springs, its direction and the winding being such as 
to produce deflection from left to right; the coil tending 
to rotate into a position at right angles to the lines of 
magnetic force, in opposition to the tension of the springs. 
And the instrument being calibrated in accordance with 
the resistance of its coils, the deflection of the pointer 
will indicate the difference of potential in volts; since 






























































































ELECTRIC MEASUREMENT. 


151 


with a given resistance the E. M. F., or potential differ¬ 
ence, varies directly as the current strength. 

The entire resistance is to that of the sectional part in 
the ratio of 20 to 1; the divisions of the scale being in 
volts for the outer reading, corresponding to the high 
resistance, and the same in twentieths of a volt for the 
inner reading, corresponding to the low resistance, as 
shown. Hence the E. M. F. which will produce a de 
flection of one division, when connection is made with 
the front binding-post on the left, will produce a deflec¬ 
tion of twenty divisions when connection is made with 
the rear binding-post. 

The high-resistance circuit is used for apparatus gen¬ 
erating strong currents, as dynamos, and the low-resist¬ 
ance circuit for apparatus generating weaker currents, 
as primary batteries, on account of its greater sensitive¬ 
ness: and as a dynamo current would be likely to injure 
or destroy the copper coil, if admitted through the low 
resistance, the rear post is protected from accidental 
contacts by an outer covering of hard rubber. In some 
of the instruments ali the posts are similarly protected; 
the rubber also preserving the contacts from* oxidation. 
The scale readings also vary in different instruments. 

The deflection of a current-bearing coil in a magnetic 
field of special strength gives the instrument great 
superiority over instruments depending on the deflection 
of a steel or soft-iron needle ; the magnetic action being 
stronger, and its relation to the current more direct. 
The constancy of the instrument is dependent solely on 
the constancy of the magnet, the springs, and the inter 
nal resistance. 

The Weston Ammeter.-— The construction of the 
Weston ammeter is similar to that of the voltmeter, but: 


THE ELEMENTS OF ELECTRIC LIGHTING . 


152 

simpler; the chief differences being that the copper coil 
is of coarser wire, having much lower resistance, and 
the resistance coil is not required: hence there are only 
two binding-posts and a single circuit, directly through 
the copper coil and springs. 

The scales for different instruments range from 5 
amperes, with divisions of ^ 0 f an ampere, to 100 am¬ 
peres, with divisions of 1 ampere, according to the rela¬ 
tive resistance of the coils. 

The Weston Milliammeter. —This instrument has the 
same construction as the ammeter, but lower resistance. 
Instruments of two different resistances, with scales of 
corresponding difference, are constructed ; one of 300 
milliamperes, with scale divisions of 2 milliamperes each ; 
and the other of 600 milliamperes, with scale divisions of 
4 milliamperes each. 

A milliampere being °f an ampere, it is evident 
that these instruments are capable of measuring very 
low currents, especially as the scale divisions are readable 
to fifths; so that the smaller instrument can indicate 
a current of ^ of 2 milliamperes, — of an ampere. 

The Wirt Voltmeter. —This instrument, illustrated 
by Fig. 66, is constructed on the principle of ascertaining 
the E. M. F. to be measured by comparison with a known 
E. M. F.; each being proportional to a resistance having 
similar conditions through which the measurement is 
made. 

The case incloses two Clark cells, each having a con¬ 
stant E. M. F. of 1.43 volts, the connections being so 
arranged that either can be employed alone, or the two 
joined in series so as to obtain an E. M. F. of 2.86 volts. 
Under the glass cover is shown a small galvanometer, 
with magnetic needle, light aluminium pointer, and 


ELECTRIC ME A S UR EMEXT. 



terminal wires connected with the coil; also a small 
scale, not shown, under the pointer, having a limited 
range, in opposite directions, from 0 at the centre. 

Extending round the case inside is a coil of german- 
silver wire, having a resistance of about 2500 ohms, one 
terminal of which is attached to one of the binding-posts 
shown on the right, marked -j- 5 while a sliding contact, 


Fig. 66. 

which can be moved to any required point on tins coil, 
is connected with the other binding-post, marked — ; 
and this contact is attached to the rim of the hard-rubber 
cap, shown above, which can be rotated on the interior 
part of the cap, on which is shown a scale graduated in 
volts, from 1| to 120. By rotating this rim, a short in- 































































































154 THE ELEMENTS OF ELECTRIC LIGHTING . 

dex, attached to it, is moved to any required point on the 
scale, the sliding contact being moved simultaneously, so 
as to include any resistance required between the ter¬ 
minals of the binding-posts. 

The galvanometer circuit also includes a certain por¬ 
tion of this coil, having a know T n resistance calibrated 
with reference to the known E. M. F. of the battery cells, 
which are also included in this part of the circuit. A 
contact key, shown on the left, closes this circuit through 
the galvanometer, producing deflection of the needle and 
attached pointer. 

If connection with a generator whose E. M. F. is to 
be measured be made through the binding-posts, so that 
the current shall oppose the meter’s battery current, the 
needle will be deflected, when the contact key is closed, so 
long as the generator current is stronger or weaker than 
that of the battery. 

Let the instrument be so placed that the earth’s mag¬ 
netism shall bring the galvanometer pointer to 0 on the 
small scale; and let the rim be turned so as to bring the 
attached index near the probable E. M. F. on the large 
scale; then, deflection being produced by closing the 
contact key, let the rim be turned so as to include sufli- 
cient resistance to equalize the opposing currents and 
bring the galvanometer pointer back to 0 ; the index 
will then show the E. M. F. of the generator in volts on 
the large scale. For since, with a given current, E. M. F. 
varies directly as resistance, if the E. M. F. of the battery 
be represented by E and that of the generator by E', the 
resistance of the battery circuit by R and that of the 
generator circuit by R', then R : R':: E:E'. That is, 
the resistance of the battery circuit is to the resistance of 
the generator circuit as the E. M. F. of the battery is to 


ELECTRIC ME A S UREMENT. 


1 55 

the E. M. F. of the generator, and the calibration gives 
this E. M. F. in volts. 

A switch is shown in front by which connection can 
be made witli either of two separate circuits, the right- 
hand contact, marked y 1 ^ to indicate the relative measure¬ 
ment of E. M. F., connecting with one having ten times 
the resistance of that connected with the left-hand con¬ 
tact. At the opposite corner, in the rear, three battery 
connections are arranged, the right and left ones, marked 
A and B , being each through a separate cell, and the 
central one, marked 2, through the two cells in series; a 
plug closing whichever connection is to be used. When 
the switch is on contact 1. as shown, and the plug in A 
or B, the scale readings require no correction, and should 
be the same with the plug in either hole, each cell being 
a check on the accuracy of the other. But when the plug 
is in hole 2, the cells being in series, the reading must he 
multiplied by 2, since the battery E. M. F. is doubled; 
for R : R ':: 27?: 2 E\ 

But wdien a generator of low E. M. F. is to be tested, 
the switch is connected with the contact marked y 1 ^, 
which includes, in the battery circuit, a resistance of ten 
times that included by contact 1; hence, since the bat¬ 
tery current with this resistance is only T J y of what it was 
with the former resistance, the E. M. F. will develop 
an opposing current of equal strength, giving the same 
reading, which must be divided by 10 to give the correct 
E. M. F.; for 107? : 7?':: 107?: 7?'. 

Each cell is If inches high and f of an inch in diam¬ 
eter. constructed with an inverted glass cup, inclosed in 
a brass case and hermetically sealed with soft rubber 
melted into the bottom. 

The electrodes are zinc and mercury, and the fluid 


156 THE ELEMENTS OF ELECTRIC LIGHTING . 

sulphate of zinc and sulphate of mercury, formed into 
a paste in which the electrodes are inclosed; connection 
with the mercury being made by an insulated platinum 
strip which represents the positive pole. 

This cell is selected on account of the remarkable con¬ 
stancy of its E. M. F., and the instrument is calibrated 
for a cell temperature of 21° C., requiring a correction in 
the reading of .000367 per degree of variation above or 
below 21° C., which must be made by subtraction for the 
higher temperature, and by addition for the lower. 

The cells are easily removed and replaced, when neces¬ 
sary, without disturbing the connections, and being small, 
hermetically sealed, and amply protected, do not inter¬ 
fere in the least with the handling of the instrument, and 
can be cheaply replaced when exhausted. 

Ayrton and Perry’s Spring Voltmeters and Am¬ 
meters. —The unreliability of electric measuring instru¬ 
ments constructed with permanent magnets, liable to 
magnetic loss, or to variation of magnetism from the 
influence of powerful currents, and consequently requir¬ 
ing frequent recalibration, has led to improved methods 
of construction, of which the spring voltmeters and am¬ 
meters of Ayrton and Perry are a result. Fig. 67 
represents the ammeter, the voltmeter being of similar 
construction ; the principle being simply the torsion of a 
spring by electromagnetic attraction. 

The current passes through a long, narrow vertical coil, 
of high resistance in the voltmeter and low resistance in 
the ammeter, within which is suspended a light soft-iron 
tube, which incloses a long spiral spring of phosphor- 
bronze ribbon. This spring supports the tube, being 
attached at bottom to a brass cap in which the tube ter¬ 
minates, and above to a milled head which rests on the 


ELECTETC ME AS UltEMENT. 


157 


glass cover and is connected with the spring by a vertical 
pin which passes through the glass; a similar pin pro¬ 
jects downward from the bottom of the brass cap and 
passes through a hole in a support below, in which it has 
a free vertical movement; so that the two pins hold the 
spring and tube in a vertical position ; and the tube being 
shorter than the coil, its centre on a vertical line is above 
that of the coil. To the top of the tube is attached a 



Fig. 67. 


light pointer which rotates over a scale graduated either 
in volts or amperes according to the design of the instru¬ 
ment. 

When no current is passing the pointer indicates zero 
on the left of the scale, but when the current passes the 







































158 


THE ELEMENTS OF ELECT RIO LIGHTING. 


tube is pulled down by magnetic attraction, in opposition 
to the torsion of the spring, to a distance proportional 
to the current’s strength; giving it a rotary motion by 
which the pointer is deflected, which indicates by direct 
readings the E. M. F. in the voltmeter, and the current 
strength in the ammeter, according to the respective 
resistance of each instrument, and its position in the elec 
trie circuit. 


The tube can be turned by the milled head so as to 
bring the pointer to the required position in calibrating; 
and a reflected image of the pointer, in a mirror placed 
under it, enables the observer to determine accurately 
its position on the scale. 

A little magnetic needle, shown at the front corner of 
the base, indicates the direction of the current; but as 
s.k h a needle is liable to have its poles reversed by 
powerful currents, a bar magnet is preferred for this 
purpose. Since the deflection of the pointer depends on 
the magnetic attraction of the tube downwards, it must 
evidently be always in the same direction, and hence in¬ 
dependent of the direction of the current; so that while 
this direction may be ascertained as above it is not 
essential to the use of the instrument that it should be 
known. 

A light movable auxiliary coil surrounds the main 
coil and is connected with it in parallel; this can ho 
moved up or down in calibrating till a position i* 
reached in which its inductive influence on the main 

coil. 1S kest adapted to the construction, where it is mad< 
stationary. 

The case is ventilated, as shown, to prevent the ac 
cumulation of heat generated by the current, which would 
expand the spring and produce inaccuracy. The usual 


EL ECTR1C 3IEA SURE31 ENT. 


159 


binding-posts connected with the terminals of the coil are 
shown at the right and left, the left post being marked A 
to distinguish them in use. 

The voltmeters are usually constructed to measure 
E. M. F. ranging from 15 volts to 1000 ; the ammeters, 
to measure current strength ranging from y 1 ^ of an am¬ 
pere to 600 amperes. 

Gravity Ammeters. —While springs have greater con¬ 
stancy than permanent magnets iu the construction of 
electric measuring instruments, their constancy is liable 
to vary, or be impaired, from well-known causes, as heat¬ 
ing, age, and use, imperfect material, or oxidation ; but 
the force of gravity, being always known and constant, 
may be utilized in such construction to produce instru¬ 
ments of great constancy. On this principle the United 
States Electric Lighting Company constructed the am¬ 
meter shown in Fig. 68. 

Two pairs of electromagnets, wound with coils of low 
resistance, and having laminated soft-iron cores, are placed 
as shown ; each pair having its coils wound on the same 
core, producing consequent poles, but magnetically insu¬ 
lated from the other pair. 

At the center, between these magnets, is mounted a soft- 
iron armature, lightly poised on a horizontal axis, the end 
of which is seen through the circular opening, and having 
a vertical rotary movement parallel to the magnets’ plane. 
This armature is about 2 inches long, inches wide at 
each end, | of an inch at the center, and | of an inch 
thick; its sides concave, and its ends convex, and slotted 
to correct the effects of residual magnetism. A pointer, 
attached to its axis, indicates the readings on a scale 
above, as shown. 

When no current is passing, the armature is main* 


160 THE ELEMENTS OF ELECTRIC LIGHTING . 

tained in a fixed position by one or more little weights 
attached to its lower left-hand corner, its longer axis 
being on a diagonal line between the lower left and 
upper right-hand corner of the instrument, and the 



Fig. 68. 


pointer at zero on the left of the scale. But when the 
current passes through the coils in either direction, the 
armature rotates in obedience to the electromagnetic 
force, its longer axis tending to assume a horizontal 










































































































































































































































































































ELECT R TO ME A S UTI EM ENT. 


161 

position, and the pointer is deflected from left to right 
in proportion to the current strength, which is indicated 
by direct reading in amperes. 

By the removal or addition of one or more of the little 
weights, the sensitiveness of the instrument may be 
varied in calibrating, as required for different ranges of 
current strength. The terminals of the coils are shown 
at the base, and holes for ventilation at the top of the 
case. 

Instruments constructed on this principle have not been 
employed to any great extent as voltmeters, not being 
sufficiently sensitive for the light currents required. 

Since the weight, as it rises, recedes from the vertical 
line which passes through its axis of rotation, the force 
opposing rotation increases in the direct ratio of the in¬ 
crease of leverage thus produced. Hence, as equal divi¬ 
sions of the scale would represent unequal increments of 
current strength, they should be made in the inverse ratio 
of this increase of leverage. 

But as it is difficult to mark off such short spaces with 
the requisite accuracy, a gravity ammeter has been con¬ 
structed by the Western Electric Company, with a ver¬ 
tical electromagnet having a pole-piece so curved that 
the rotating armature, as it rises, constantly approaches 
it, the magnetic attraction increasing in the same ratio as 
the leverage, so that equal divisions of the scale represent 
equal increments of current strength. 

The Cardew Voltmeter. —The instruments thus far 
described are designed to be used with direct currents, 
and are liable to errors arising from self-induction in 
addition to those from the other causes mentioned. But 
since, according to a well-known law, the heat developed 
in an electric conductor is in direct proportion to the 


162 


THE ELEMENTS OF ELECTRIC LIGHT INC. 


square of the strength of the current passing through it, 
instruments can evidently be constructed on this princi¬ 
ple which will measure either current strength or differ¬ 
ence of potential, produced either by direct or alternating 
currents, and are not liable to variation from any of the 
causes mentioned. Among these the voltmeter, patented 
by Cardew in 1886, has a prominent place. Its operation 



depends on the expansion of metal produced by the elec¬ 
tric development of heat. 

Fig. 69 gives a front view of this instrument and Fig. 
70 a rear view, showing its internal construction. A fine 
platinum wire, 8 feet lung, is stretched in four lengths 
in a horizontal tube, by attachment to a metal frame 



















ELEC TJtIC ME A S UREMENT. 


163 

and pulleys, as shown at a a tt in Fig. TO. This tube is 
made of very thin metal, one third of its length being 
iron and two thirds brass to maintain constancy of length 
between the points of attachment of the wires by such a 
mode of connection as to produce compensation by the 
unequal expansion of the two metals; and the horizontal 
position is given it to maintain constancy of temperature, 



Fig. 70. 


and prevent the unequal expansion, from convection of 
the air to which the tube and wire would be liable in a 
vertical position. 

The wire has a resistance of about 240 ohms, and at¬ 
tains a maximum temperature of about 200° C.; and its 






































164 


THE ELEMENTS OF ELECTRIC LIGHTING. 


expansion varying in a certain definite ratio dependent on 
the difference of temperature caused by the passage of 
the electric current, which, as stated, varies as the square 
of the current’s strength, produces a variation in length 
proportional to the E. M. F. by which the current is 
generated. This produces a rotation in the pulley w, to 
the axis of which the pointer shown in Fig. 69 is attached, 
which moves in the same direction as watch-hands when 
theE. M. F. increases, and in the opposite direction when 
it decreases. 

The scale is graduated to correspond to the expansion 
of the wire ; its divisions varying in size, as indicated, in 
proportion to the variation of ex-pansion produced by the 
unequal variation of temperature, in the ratio of the 
square, with equal variation of current strength, and 
consequently of E. M. F., since resistance remains con¬ 
stant. 

This instrument should be calibrated for the average 
temperature of the room in which it is to be used. 

The Edison Current Meter. —This is a commercial 
instrument constructed on the principle that the quantity 
of current consumed on a lamp circuit is in direct pro¬ 
portion to the quantity of metal deposited by electrolysis 
by a small current from the same source, passing at the 
same time, through a shunt. 

Fig. 71 shows the construction. There are two cells, 
intended respectively to show the monthly con¬ 
sumption, and the consumption for a longer period, the 
one to act as a check on the other; each cell contains 
amalgamated zinc plates immersed in a solution of zinc 
sulphate, both having precisely the same construction. 
Underneath each is a corrugated band of German 


EL K critic ME AS UIt EMENT. 


165 

silver; tlie twelve corrugations at the left, marked m>, 
forming the shunt through which current flows to the 
cell p; and the four at the right, that through which 
current flows to the cell which consequently receives 
four times the current through one-fourth the resistance. 

As the deposition of metal varies with change of 
temperature, apparatus for equalizing the temperature, 
and compensating the effects of variation, becomes 



Fig. 71. 


necessary. The general temperature of the instrument 
is equalized by the lamp l c l9 above which is the com¬ 
pound bar fc. When the temperature falls below 
the normal degree, this bar bends down, closing the 
circuit through the contacts c, c h and lighting the 
lamp: as the temperature rises, this circuit is opened 
by the upward bending of the bar, and the lamp is 
extinguished. 

But as rise of temperature by the chemical re-action 



























































































the elements: of electric lighting. 


of the cells increases the conductivity of the solutions, 
the compensating copper coils, w, w v are placed in 
circuit under each cell respectively. The increase of 
current through each coil, caused by increase of con¬ 
ductivity in the solution, raises the temperature of the 
coil, and reduces its conductivity: lienee, by making 
the length of each coil such that its temperature shall 
vary in the same ratio as that of the solution, compen¬ 
sation is effected; the rise of temperature in the coil 
reducing its conductivity, and diminishing the current, 
in the same ratio as the rise of temperature in the 
solution increases its conductivity, and vice versa. 

These cells are removed and renewed at stated peri¬ 
ods, the zincs weighed, and the amount of current 
consumed estimated by the amount of zinc deposited. 
One of the cells is accessible to the consumer, and 
monthly inspector; while the other is examined only 
by the higher inspector at the close of the longer 
period, and the results compared and corrected; the 
deposition of zinc in each respectively for the different 
periods being practically the same in consequence of 
the difference in supply of current. 

The Forbes Coulomb-Meter.— Meters like the Edi¬ 
son cannot be used for the measurement of alternating 
currents; but one has been invented by Forbes, operated 
by the heat developed by the current, which can meas¬ 
ure either direct or alternating currents. Its construc¬ 
tion is shown in Fig. 72. The current passes through a 
flat coil of iron wire, above which is mounted, on a 
paper cone having a jewelled bearing at its apex, a mica 
disk, with mica vanes attached. The heat developed 
by the current produces an ascending current of air 
which rotates the disk, operating a light train of clock- 


ELECTRIC MEASUREMENT. 


167 

work which moves indexes over two dials, registering 
the current consumption in coulombs; units being 
registered on one dial and tenths on the other. A 
glass shade protects the apparatus from external air- 

currents. It has never come into practical use. 



Fig. 72 . 


The Thomson Recording Watt-Meter.— Since both 
E. M. F. and current strength are included in electric 
energy, a meter for commercial use should record their 
joint product as represented by the watt. Fig. 72|- shows 
such a meter, invented by Elihu Thomson. 



































168 TIIE ELEMENTS OF ELECTRIC LIGHTING. 

Two field-coils, A and B , composed of heavy copper 
wire, varying in diameter from f of an inch upward, 
according to the required capacity of the meter, are 
mounted as shown, about J of an incli apart. They are 
wound without cores, both in the same direction, in 
series with each other and with the electric mains; the 
winding being in vertical planes, parallel to the open 
ends, and hence at right angles to that of the exterior 
cloth covering shown in the cut. 

They inclose a drum armature of the Siemens type, 
seen through the opening on the left, composed of eight 
to sixteen coils of fine copper wire wound vertically, 
in a closed circuit, on a light frame of non-magnetic 



Fig. Wf 


material, and mounted on a vertical shaft, the terminals 




































ELECTRIC ME A N (IREMENT. 


169 

of each coil being attached to adjacent segments of a 
silver commutator, mounted on the shaft just above the 
armature. 

The field-coils, being in series with the mains, carry a 
current of the same strength, while the armature, which 
is on a fine wire shunt between the mains, carries only a 
small percentage of this current, representing the E. M. F. 
at this point, and equal, at average normal electric press¬ 
ure, to about y 1 ^ to y 1 ^ of an ampere, but varying accord¬ 
ing to pressure and capacity of meter. Hence the mutual 
induction of the two currents represents the joint product 
of E. M. F. and current strength, the two factors of elec¬ 
tric energy included in the watt. 

The shunt current enters and leaves the armature by 
two silver-tipped copper springs which constitute the 
brushes, and press against opposite segments of the 
commutator on the neutral line between the field- 
coils, as in the dynamo; rotation of the armature being 
produced by the magnetic polarity induced in the 
field and armature coils respectively, as in those having 
iron cores. This polarity is similar on adjacent sides 
of the field and armature, and opposite on opposite 
sides; hence each half of the armature is repelled from 
that side of the field having similar polarity and attracted 
to that having opposite polarity ; and the direction of the 
current in each armature-coil being reversed by the com¬ 
mutator, on the neutral line, at each half-revolution, the 
rotation is made continuous. The mode of action is the 
same as that of the electric motor, or reversed dynamo, 
current producing rotation, instead of rotation producing 
current as in the dynamo. 

As reversal of current in the field-coils would produce 
corresponding reversal in the armature coils, the relative 


170 


THE ELEMENTS OF ELECTRIC LIGHTING. 


direction of current in each, and hence the relative po¬ 
larity, would remain the same, producing rotation in the 
same direction as before reversal. Hence an alternating 
current produces continuous rotation in the same manner 
as a direct current, reversal being simultaneous in the 
field and armature. 

The shunt current traverses a german-silver resistance 
coil in the back 6 y , by which its strength and relative 
E. M. F. may be varied inversely as required; and in 
meters designed for circuits of very high potential, as 
1000 volts, it passes also through a small transformer by 
which its E. M. F. is reduced. 

The shunt circuit being connected to the mains between 
the field-coils in most of the meters, its current traverses 
the armature in series with that of the field-coils, instead 
of in parallel, as it would if the shunt connections were 
outside of the field-coils ; and a slight additional strength 
of field, and hence of rotary force, is thus gained, which is 
of importance in compensating friction at low speed of 
the armature, when the ratio of friction to rotary force is 
large. 

The armature rests in a jewelled bearing, by which its 
friction is reduced to a minimum. Near its upper end 
it carries an endless screw which engages a train of gear¬ 
ing by which five pointers are rotated, at different rates 
of speed, over dials having ten divisions each, record¬ 
ing the energy consumed in watt-hours, on a decimal 
scale, ranging from 10,000,000 on the left-hand dial to 
1000 on the right-hand dial; each indicating a decimal 
part of that indicated on the next preceding dial to the 
left. A watt-hour represents the electric energy of a 
current of one watt flowing for one hour, or its eauiva- 


ELECTRIC MEASUREMENT. 

lent for any fraction of an hour, as a ten-watt current 
for a tenth of an hour. 

Attached to the shaft, near its lower end, is a copper 
disk, 71, which rotates between the poles of three mag¬ 
nets, generating an opposing force by which the speed of 
the armature is limited and controlled, and which varies 
as the number of lines of force cut by the disk per unit 
of time, and therefore in the same ratio as the speed. 
This prevents excessive speed, also speed due to mechani¬ 
cal momentum in excess of electric energy, and puts the 
apparatus under the control of opposing forces generated 
solely by the electric energy, and therefore correctly rep¬ 
resenting it. 

By increasing or diminishing the distance of the mag¬ 
nets’ poles from the centre, the retardation can be cor¬ 
respondingly increased or diminished, and the speed 
regulated as required in calibration. Magnetic loss can 
also be thus compensated when recalibration is required. 
This loss is slight, however, as the constancy of the mag¬ 
nets is improved by a special seasoning before they are 
put in use. 

These meters vary in minor details of construction, 
with reference to their capacity and the use for which 
each is designed; and they are thus adapted to different 
systems of electric distribution, and to direct or alternat¬ 
ing currents ; those intended for direct currents requiring 
non-magnetic frames. They range in current capacity 
from 10 amperes to 150, and in potential capacity from 
50 volts to 2000. 

Measurement of Electric Resistance. —Since cur¬ 
rent strength depends on the mutual relations of electro¬ 
motive force and resistance, it is evident that apparatus 
for varying resistance by the introduction or withdrawal 
of a definite known quantity, and of ascertaining and 


172 


THE ELEMENTS OF ELECTRIC LIGHTING. 


measuring it when unknown, in order to property adjust 
these mutual relations, is a matter of the highest im¬ 
portance in electrical construction. Resistance may he 
varied, as already shown, by varying the length or diam¬ 
eter of the conductor, or by changing the circuit from 
series to parallel or the reverse; but as this usually re¬ 
quires permanent construction, it becomes necessary to 
have also some simple means by which a resistance of 
known amount can be property introduced into any cir¬ 
cuit or withdrawn from it without interference with the 
permanent construction: this is furnished by the resist¬ 
ance coil , or rheostat, as it is also termed. 

Resistance Coils. —Resistance coils are made of ger¬ 
man-silver wire on account of its high resistance, which 
is usually about seventeen times that of pure copper, and 
calibrated as to gauge and length for a given number of 
ohms resistance, the wire being property wrapped for in¬ 
sulation. Fig. 73 gives an ideal view of the construc¬ 
tion. 


X, Y, and Z are short blocks of brass, insulated from 
each other above, but connected below through the coils 

c and d , as shown ; each coil 
being wound with a double 
strand to reduce self-induction. 
] Two brass plugs, a and b , hav¬ 
ing hard-rubber handles, tit 
into holes between the blocks, 
so that when placed as shown, 
the three blocks are in electric 



Fig. 73. 


connection, and having practically no resistance, a current 
would pass directly through them, without traversing 
the coils. But if a plug, as is removed, the current 
between X and Y must then pass through the coil c. 








ELECTRIC MEASUREMENT 


173 


In like manner if ping b is removed, the current between 
Y and Z must pass through the coil d ; which, being 
twice the length of c, would have twice the resistance if 
made of wire of the same gauge, or four times the re¬ 
sistance if also the cross-section of the wire was one half 
that of c. In this way resistance can be varied to any 
practical extent required. 


Sets of resistance coils, calibrated for resistance vary¬ 
ing from 1 ohm or less to 10,000 or more, are con¬ 
veniently arranged in cases, as shown in Fig. 73-J. The 



Fig. m . 

case has a hard-rubber cover by which the brass blocks 
are insulated above, each pair being connected through a 
coil below, as shown in Fig. 73. A hole in the centre of 
each block receives each plug when removed from be¬ 
tween the blocks, to prevent its being mislaid, and con¬ 
nection with the electric circuit is made through the bind¬ 
ing-posts shown at the right. 

To introduce any required resistance it is only neces¬ 
sary to remove the plug from its place between the blocks 
opposite which the resistance required is marked on the 





















































174 


THE ELEMENTS OF ELECTRIC LIGHTING. 


cover, the other plugs all remaining connected. If, for 
instance, 1 ohm resistance is to be introduced, let the first 
plug at the front right-hand corner be removed, opposite 
which “ 1 ohm” is marked ; the current must now flow 
through that coil, and pass by all the other coils, through 
the blocks and plugs; if 50 more ohms are to be added, 
the last plug at the rear left-hand corner is removed, op¬ 
posite which is marked “ 50 ohms;” and the resistance 
then becomes 51 ohms. 

The Standard Light Unit.— The illuminating power 
of a lamp is determined by the photometer, bv com¬ 
parison with a standard unit of light. This standard 
varies in different countries. In France it is the Car- 
cel lamp, in which pure colza oil is burned; the wick 
being 30 millimeters in width, and the flame 40 milli¬ 
meters in height. The German standard is a paraffin 
candle, 20 millimeters in diameter, having a flame 50 
millimeters in height. The English standard is a sperm 
candle, burning 120 grains per hour. The Paris Elec¬ 
tric Conference of 1881 adopted as a standard unit the 
light radiated by a centimeter of pure melted platinum 
at the temperature of congelation. A platinum strip 
5-6 millimeters wide is inclosed in a metal box having 
a conical opening of 1 square centimeter at its narrow¬ 
est part, and is brought to the point of fusion by a 
battery current; the radiated light being just one-tenth 
that of the standard unit. A lamp or candle whose 
illumination has been determined by this unit, can be 
most conveniently used in practice. 

The Bunsen Photometer. — Every photometer is 
constructed according to the well-known law, that the 
intensity of light varies inversely as the square of the 
distance ; the light being received by the instrument at 


EL EC T It IC ME A S UREMENT. 


175 


a certain definite angle. Of the various instruments 
of this kind in use, the Bunsen is one of the simplest 
and most practical. A convenient style of this instru¬ 
ment consists of a narrow box about forty inches in 
length, with sliding shutters on one side : in it is placed 
a little screen of oiled paper mounted on a movable 
frame between two mirrors, at equal angles to both, 
so that an illuminated spot on the screen can he seen 
at the same time in both mirrors. This screen, with 
the mirrors, slides longitudinally, and can be moved to 
any required point on the central axis of the box, and 
inspected through an opening in the shutters. The 
standard light is placed in one end of the box, and the 
light to be measured in the other end, air holes being 
provided above each. The screen is then moved to a 
point where the intensities of the opposite lights, as 
seen by their reflected images in the. mirrors, are equal, 
which requires careful adjustment till the variation in 
illumination is equalized. The exact distance of each 
light from the screen being shown on a graduated scale, 
the illumination of the light under measurement, as 
compared with the standard, is determined by the law 
given above. If the distance of an incandescent lamp 
from the screen is four times that of a standard candle, 
then the candle power of the lamp is 4x4 =16 
candle-power. 

If an arc light is to be measured, the required dis¬ 
tance from the screen being too great to admit of the 
use of the box, the measurement must be made in a 
darkened room of sufficient length. 


CHAPTER VII. 


The Arc Lamp. 

Principles of the Arc Lamp. — The production 
of light and heat by the electric current depends prima¬ 
rily on the strength of the current, and on the resist- 
tance which it encounters; the development of heat in 
a conductor, according to Joule, being proportional to 
its resistance, to the square of the strength of the 
current, and to the time the current lasts. We have 
illustrations of this in the spark of the electric machine 
and in the lightning’s flash, both of which result from 
the resistance of the air to the passage of electricity. 
Heat is always a result of this resistance, even in the 
best conductors, and precedes the production of light; 
but the resistance encountered in such conductors as 
copper and iron is not sufficient, except with currents 
of abnormal strength, to raise the molecular intensity 
to the degree requisite for the production of light. 
The case is analogous to that of the production of 
heat by friction, where heat development is in the 
inverse ratio of heat conductivity: friction between 
wooden surfaces rapidly produces combustion, the 
effect being, from want of conductivity, concentrated 
on the points in contact; while from the conductivity 
of metals the heat developed by the same amount of 
friction is distributed through the mass, and the tem¬ 
perature developed at the points of contact prop or* 


THE ARC LAMP. 


1 77 

tionally reduced, the proportion depending on the 
conductivity of the metals. Similarly, what takes place 
on the surface in mechanical friction may be assumed 
to take place throughout the mass in the molecular 
action which we term electricity. And if, as we have 
assumed, electric conductivity depends on molecular 
arrangement, the internal friction between the mole¬ 
cules must be greater in an abnormal arrangement, 
such as may be assumed to exist in substances of low 
conductivity, than in the normal arrangement assumed 
to exist in those of high conductivity. Hence the 
choice of a substance having the proper proportions of 
conductivity and resistance combined with other neces¬ 
sary qualities becomes an important consideration in 
the construction of the electric lamp. 

There are two methods of producing the light, one 
depending on the combustion of the light-producing 
substance, and the other on its incandescence ; and these 
methods have given rise to two systems known respec¬ 
tively as the arc light and the incandescent light 
systems. The arc light is the oldest, and originated 
with Sir Humphry Davy in 1813 ; and it is remarkable 
that carbon, the substance in common use in the modern 
electric lamp, was the substance which he adopted in 
those early experiments; and the construction of the 
modern lamp has for its principal basis the same funda¬ 
mental principles which he discovered and adopted. 
Passing a current furnished by a battery of 2,000 
voltaic cells through two rods of common wood char¬ 
coal, placed end to end, he obtained, on slightly sepa¬ 
rating them, a light of intense brilliancy and heat, 
having the form of an arch, or arc of a circle; hence 
the term voltaic arc, designating both the origin and 


178 THE ELEMENTS OF ELECTRIC LIGHTING. 

form of the light, the latter word being still retained, 
while the former lias fallen into disuse since the 
battery, as a generator for lighting purposes, has been 
superseded by the dynamo. 

The contact of the carbons is necessary for the 
establishment of the current, and their subsequent 
separation for the production of the light. The ordi¬ 
nary current which maintains the light is not strong 
enough to pass through an air space of even iq JoI) 
an inch ; but the current produced by the separa¬ 
tion of the carbons after contact is far more powerful, 
resulting from the difference of potential caused by 
the sudden accumulation of energy on the positive 
side of the break, and the negative condition on the 
opposite side: a film of carbon is volatilized by this 
powerful current, and the space between the carbons 
filled with carbon vapor, which is a partial conductor 
of very high resistance. The combustion of this vapor, 
and of the carbons themselves by the union of oxygen, 
heats the air, and reduces its resistance, so that the 
current is maintained in this heated air and vapor 
at its normal strength through a resistance varying 
from an ohm to 100 ohms, and across an air space 
of y i6 to % inch. The light is of intense brilliancy, 
varying from 1,000 to 2,000 candle-power, being greatest 
on the surfaces of the carbon points, especially on that 
of the positive carbon; while the heat, which is also of 
great intensity, is greatest in the carbon vapor, and 
capable of volatilizing the most refractory substances, 
not excepting even the diamond. 

T1 le direct current is usually preferred for the arc light, 
and the vertical position for the carbons; the current 
passing from the upper to the lower carbon, as shown 


THE ARC LAMP. 


179 

in Fig. 74. The upper, or positive, carbon is consumed 
about twice as rapidly as the lower, or negative, carbon ; 
and the exterior of both more rapidly than the inter ior; 
consumption increasing toward the tips, producing a cone 
on each, the lower pointed,and the upper truncated, with 
the formation of a crater at the tip. The light, being the 



Fig. 74. 


most intense on the upper carbon surface as stated, ema¬ 
nates chiefly from this crater, and is radiated downward; 
the amount thus radiated being equal to about sixty-five 
per cent of the entire light produced. This is the prin¬ 
cipal reason why the direct current is preferred for arc 
lighting; illumination, except in special cases, being 
wanted below rather than above or in a horizontal 



180 


THE ELEMENTS OF ELECTRIC LIGHTING. 


direction, especially from arc lights, which, from their 
intense brilliancy, and the powerful currents which they 
require, must be elevated for safety. 

With the alternating current, both carbons are con¬ 
sumed at the same rate, and both retain the pointed 
form, which permits a free radiation of the light in 
nearly every direction. For lighthouse illumination, 
there is an advantage in this; and by reflectors and 
lenses, the light can be concentrated and intensified in 
a given direction. While there would seem to be an 
economical advantage in the equal consumption of the 
carbons by the alternating current, it has been ascer¬ 
tained by experiment that the carbon wastage is much 
less with the direct current. 

In short arcs, particles of carbon and fused impurities 
are deposited on the lower carbon, forming the mush¬ 
room tip shown in Fig. 74, which is burnt off at the 
base and again renewed, as the consumption pro¬ 
ceeds. This deposit does not occur in long arcs. 

The flame assumes the form of an arc from the fact 
that the electric potential of the space between the 
carbons is much higher than that of its surroundings, 
including the air and external objects; consequently 
the incandescent vapor is repelled from this space by 
virtue of equality of potential within the space, and 
attracted outward by virtue of difference of potential 
between the space and its surroundings; and the flame 
beiim connected with the carbons above and below, the 
central part alone yields to this outward pressure, pro¬ 
ducing the arc. 

Since the alignment of the carbons is not exact, nor 
the surfaces in contact perfectly flat, the flow of the 


THE ARC LAMP. 


181 


current before separation is liable to be through points 
at one side of the center ; and after separation and the 
formation of the crater, the line of least resistance is 
evidently between the point of the lower carbon and 
the lowest point on the edge of the crater. The high- 
est potential is evidently through the center of the 
flame, where the principal part of the current is flowing; 
and the outside potential being lower than the potential 
at any point between the carbons, the flame bends out 
to one side, instead of equally on all sides, and forms 
an arc; whereas, if the current were perfectly central, 
and the outward pressure perfectly equal on all sides, 
the flame would be a spheroid. 

As each lowest point on the edge of the crater is 
consumed, and the distance, and consequently the re¬ 
sistance, is increased, the flame shifts to the next lowest 
point, and so travels round the edge of the crater while 
pivoted on the point of the lower carbon. 

As an electric current can be attracted or repelled by 
a magnet, this flame-bearing current exhibits the same 
effects; and the arc can thus be increased or diminished 
by the approach of a magnet, and also be attracted by 
the approach of an unmagnetic body of different elec¬ 
tric potential. 

Arc Light Carbons. — As the efficiency of the 
electric light depends very largely on the carbons, it is 
of the highest importance that they should be properly 
prepared; hence not only the materials of which they 
are composed, and the methods used in their prepara¬ 
tion, require careful consideration, but their length, 
diameter, conductivity, resistance, and other points, are 
also matters of the utmost importance in securing the 
best results. 


182 THE ELEMENTS OF ELECTRIC LIGHTING . 


As already stated, wood charcoal was the substance 
employed by Sir Humphry Davy; but this in its ordi¬ 
nary state is unsuitable, being soft, porous, and rapidly 
consumed, with a deflagration troublesome and danger¬ 
ous : it therefore became necessary to find some form 
of carbon which would consume slowly, and give a 
steady, brilliant light. The carbon cut from the inte¬ 
rior of gas retorts, was proposed by Foucault, and was 
found to fulfill these conditions to a certain extent; but 
its impurity, and lack of homogeneousness, interfered 
seriously with the quality and steadiness of the light, 
though, for want of something better, it was used in 
all the early experiments; but it became evident that 
carbons specially prepared for this purpose were required, 
and this requirement became the more imperative when 
electric lighting, by the invention of the dynamo, was 
made a commercial success. Various experiments by 
different European inventors finally resulted in the pro¬ 
duction in France of the carbons of Carre and Gaudoin, 
which were the first to fulfill approximately the 
required conditions of purity, homogeneity, proper 
resistance, and proper form. 

Previous experiments in this direction by Lacassagne, 
Thiers, and others, had been made in 1857 and subse¬ 
quently, by pulverizing and purifying the carbon, 
making it into a paste, molding and baking it. One 
of the early methods of Gaudoin was to use rods of 
wood charcoal, similar to those employed by Davy, 
infiltrate them with various hydrocarbons by repeated 
soaking and baking alternately till they had attained the 
necessary consistence as indicated by their metallic ring. 

The Carr<$ carbons, which still maintain a hicdi 
standard of excellence, are now made as follows: Fifteen 


THE ARC LAMP. 


183 


parts of pure coke finely pulverized, and five parts 
of calcined lampblack, are mixed with seven to eight 
parts of a syrup made of cane sugar and gum arabic, in 
the proportions of thirty parts of sugar to ten parts of 
gum. The mixture is then pulverized, made into a 
paste with water, forced under heavy pressure into 
a die of the form required for the carbons, and baked 
repeatedly at a very high temperature. After each 
baking the carbons are immersed in a concentrated 
syrup of burnt sugar, maintained at a boiling tempera¬ 
ture, so as to fill the pores with the sugar, the process 
being facilitated by intervals of cooling; and the super¬ 
fluous syrup being washed from their surfaces with 
boiling water previous to each baking. When the 
required density is attained, the carbons are slowly 
dried for about fifteen hours at a temperature of about 
170° C., and are then ready for use. Great tenacity is 
one of the good qualities claimed for these carbons, and 
they can be used in lengths of twenty inches without 
risk of fracture. 

The Gaudoin carbons are made from carbon obtained 
by the destructive distillation, in closed graphite cruci¬ 
bles, of tar, bitumen, pitch, oil, and other substances; 
all foreign matter being expelled, leaving a residuum of 
nearly pure carbon. 

This is reduced to a fine powder, made into a paste, 
and the carbons formed under a high pressure. 

Napoli, another French manufacturer, makes his 
carbons from a coke obtained from the slow distillation 
of coal. This coke, after being pulverized and screened, 
is mixed with gas tar, in the proportion of seventy-five 
per cent of the coke to twenty-five per cent of the tar. 
The carbons, after being formed, are first baked at a 


184 THE ELEMENTS OF ELECTRIC LIGHTING. 

low temperature, not exceeding that at which the coke 
and te were produced: after cooling they are baked 
again at a white heat, which removes all traces of gas, 
producing carbons of great hardness, ready for use with¬ 
out further treatment, which are said to give a steady, 
pure white light at a slow rate of consumption. 

In the manufacture of the Liepmann carbons, made 
in London, the raw material is obtained from the dis¬ 
tillation of mineral oil, which, it is claimed, contains 
only carbon and hydrocarbons, and furnishes carbons 
free from the impurities found in those made from coke, 
graphite, or retort carbon, which produce the colored 
tints and flickerings in the light, and the troublesome 
ash deposit. The material is soft and brittle, and 
easily pulverized. It is first ground to a fine powder, 
then baked, and subsequently mixed with a specially 
prepared tar, and the paste thus formed, molded into 
carbons. The molding is done under a pressure of 
about thirteen thousand pounds to the square inch, 
obtained from a hydraulic accumulator in connection 
with a steam-engine and pump. The carbon rod, 
squirted endways through a die, issues continuously 
upon a table moved on rollers; and, when a length of 
four feet is attained, it is cut into twelve-inch lengths 
by four knives carried in a frame. The carbons are 
then stacked, with carbon dust between the layers to 
prevent adhesion, dried in the air for several weeks, 
and then straightened by being rolled between boards, 
after having been sufficiently heated to render them 
plastic. Two kinds are prepared in this way, — the solid 
carbons, and the shells for cored carbons. These shells 
are closed at one end, and the cores injected by a small 
hydraulic press. 


THE ARC LAMP. 


1S5 


^ The baking, which is an exceedingly important and 
uelicate operation, is done in gas-heated furnaces in 
which the heat can be kept under perfect control. The 
caibons, stacked upon an iron trolly, are slowly passed 
through the principal furnace, which has five zones of 
heat: they enter through the coolest zone, and emerge 
through the hottest, and then pass into an auxiliary 
furnace, the temperature of which is reduced very 
slowly. They are then finished by trimming the ends, 
and copper plating such as require it, and, after being 
tested for resistance, are ready for use. 

The testing is accomplished by an automatic machine, 
electrically controlled, through which the carbons are 
passed ; each one being momentarily inserted in a shunt 
to a solenoid. The required resistance of a carbon 
being about two-tenths of an ohm, if the resistance 
exceeds this, the carbon is held, carried forward, and 
dropped into the box of rejected carbons ; but if the 
resistance is less, permitting a greater flow of current 
through the carbon, the current through the solenoid is 
reduced; and by means of a spring, which opposes the 
attraction of the solenoid, the carbon is released, and 
drops into another box. 

The copper plating is accomplished by an apparatus 
having eight sliding frames, each carrying a row of 
spring clips by which the carbons are suspended, and 
under each frame a glass vessel containing dilute sul¬ 
phuric acid in which a copper cylinder is immersed; 
this cylinder forms one of the electrodes; and the frame, 
when lowered and immersed in the liquid, forms the 
other. The current is furnished by a dynamo, which 
also supplies the current for the testing machine, con¬ 
nection being made by an automatic switch when the 


180 THE ELEMENTS OF ELECTRIC LIGHTING. 

frame is lowered; and the time required for plating is 
indicated by the color of the deposit. 

In the United States the material now used in the 
manufacture of arc light carbons is petroleum coke, a 
residuum of the distillation of crude petroleum, which 
contains very little foreign matter that cannot be ex¬ 
pelled by heat. This is ground and mixed with some 
hydrocarbon, generally gas-house pitch, and the mix¬ 
ture then ground again. It is then placed in steel 
molds of the proper form, twelve inches long, and 
heated sufficiently to render it plastic, after which it is 
subjected to a hydraulic pressure of from 3,000 to 8,000 
pounds to the square inch; the amount of pressure de¬ 
pending on the purpose for which the carbons are 
intended. They are then baked at a high temperature for 
24 to 100 hours, according to the style of furnace, and 
number of carbons placed in it. The crooked carbons 
are then culled out, and the straight ones electroplated. 

It has been shown that the arc light is derived from 
incandescent carbon, and carbon vapor; also that, in the 
process of manufacture, various hydrocarbons are used, 
both in the original composition and in the subsequent 
process of infiltration, after which the carbons are again 
baked at a high temperature ; the object of the infiltra¬ 
tion being to produce density, and of the subsequent 
baking to reduce the hydrocarbons to pure carbon by 
expelling the other constituents. 

It is found that the intensity of the light is in the 
direct ratio of the temperature of the arc; and, since 
pure carbon requires for its volatilization the highest 
temperature of any known substance, it is evident that 
this intensity depends on the purity of the carbon, any 
remaining foreign substance becoming volatilized at a 


TEE ARC LAMP. 


187 


lower temperature, and interfering seriously with the 
intensity of the light. It is shown by the spectroscope 
that the whiteness and purity of the light depends, like 
its intensity, on the purity of the carbon ; and it is also 
' found that the resistance of the arc is in the same ratio ; 
its resistance being at the maximum, and its conduc¬ 
tivity at the minimum, with the maximum of purity 
in the carbon. The distance between the carbons, as 
will be shown hereafter, is regulated automatically by 
this resistance, being shortest when the resistance is 
greatest; and the consumption of the carbon is, at the 
same time, at the minimum. Hence it follows that 
the highest economy of consumption, and the best light 
is attained with the greatest purity of the carbon. 

As the vapor resulting from the volatilization of for¬ 
eign substances has higher conductivity than carbon 
vapor, there is often, with impure carbons, a sudden 
lengthening of the arc and reduction of the light, caused 
by the consumption of this foreign material, the carbons 
automatically adjusting themselves to the reduced resist¬ 
ance, and again returning to their normal distance, and 
the light to its normal intensity and purity, when the 
foreign matter is consumed; the net result being a 
flickering, unsteady light, varying from a short arc of 
intense brilliancy to a long colored arc of perhaps one- 
fourth the brilliancy, and returning again to the intense 
white arc. 

0 

Another serious defect is the lack of homogeneousness 
of structure, even with purity of material; the density 
at the ends may vary materially from the density at the 
center, producing an irregular rate of consumption; or 
dense carbon may be infiltrated throughout with soft 
carbon, the soft carbon consuming more rapidly, pro- 


188 THE ELEMENTS OF ELECTRIC LIGHTING. 

ducing numerous small craters, and leaving ridges of 
hard carbon, resulting in a noisy, inconstant light. Car¬ 
bons molded by side pressure are less liable to the first 
defect — difference between the density of the ends and 
center — than those molded by end pressure, and sub¬ 
sequently cut into lengths; and the latter method has 
been generally abandoned in favor of the former in 
American factories, as it was found impossible to apply 
end pressure with proper uniformity. Carbons with the 
cores injected into shells of greater density, burn more 
rapidly in the center than at the edges; and hence the 
form of the crater is more perfect, and the liability to 
the second defect — small craters surrounded by hard 
ridges — is greatly reduced. This defect can also be 
overcome by proper care in the preparation of the paste. 

Carbons require to be perfectly straight and cylindri¬ 
cal, and of perfectly uniform diameter from end to end; 
and those of the length required for the usual long 
periods of continuous consumption are liable to defects 
in one or more of these respects in the various processes 
of manufacture. Good contact with the carbon holders, 
and proper alignment of the two carbons, is impossible 
with those of defective form ; and such carbons are a 
constant source of annoyance, no matter how great their 
excellence as regards purity and density. 

The electric resistance of the carbons is also a point 
of the highest importance, especially on a circuit having 
a large number of arc lamps in series ; and here again 
the purity of the carbons becomes important, for while 
the resistance of the incandescent vapor which consti¬ 
tutes the arc increases with the purity of the carbon, as 
has been shown, the resistance of the carbons themselves 
diminishes; the purest and densest carbons having the 


THE ARC LAMP. 


189 


nwest resistance. Plating with copper, iron, or nickel, 
tor the purpose of reducing resistance, has been tried 
with varied success, also embedding iron wire in the 
'enter of the carbons. The principal objection to 
sopper plating is, that with the direct current, the 
tarbon of the negative rod is consumed more rapidly 
than the copper, leaving a copper fringe which casts a 
shadow ; but, notwithstanding this objection, it is gen¬ 
erally adopted as the best means of reducing resistance. 
Carbons for lights not exceeding 1 1,200 candle-power 
do not require plating, while those for lights of 2,000 
candle-power and upwards are always plated. 

The ordinary length of carbons, as already stated, is 
12 inches; but the diameter varies according to the 
strength of current and candle power of the light for 
which the carbons are intended, ranging from 7 / 16 inch 
with a 6.8 ampere current, and a 1,200 candle-power 
light to Vie inch, with a 15 ampere current and a 3,000 
candle-power light. For a 2,000 candle-power light 
with a 10 ampere current, the diameter of the carbons is 
Vie to 8 / 16 inch; while for exceptionally powerful lights, 
such as are required for lighthouses, and search lights 
on steamers, carbons exceeding an inch in diameter are 
required. 

The principle which underlies this is the ratio of 
molecular action to the mass of the carbon. If the mass 
is too small for the amount of current, the molecular 
action is too much concentrated, and the carbon either 
wastes away by becoming heated through from end to 
end, or there is an imperfect formation of the crater, the 
edges consuming too rapidly, allowing upward radia¬ 
tion, and consequent practical loss of light. But if the 
mass is too large for the current, the molecular action 


190 THE ELEMENTS OF ELECTRIC LIGHTING. 

is too much diffused, producing a dull red light in the 
outer portions of the carbons instead of an intense in¬ 
candescent glow; the point of the lower carbon also 
becomes too obtuse, causing too great lateral radiation, 
and a broad shadow underneath. With the proper pro¬ 
portions between the amount of current and the diam¬ 
eter of the carbon, the increase of light is in the direct 
ratio of increase of diameter; powerful lights requiring 
carbons of large diameter, while smaller lights require 
those of less diameter. 

The Jablochkoff Electric Candle.— -Among 
the earlier methods of producing the electric light was 
the candle invented by Jablochkoff, a Russian military 
officer, in 1872, about five years subsequent to the in¬ 
vention of the Gramme dynamo ; and its use had been 
continued up to a comparatively recent date, 2,500 of 
these candles being used in Paris for street lighting as 
late as 1880; and though finally superseded by better 
methods, it will always possess a historical interest on 
account of its success and popularity in the early history 
of electric lighting. 

Its construction is exceedingly simple, consisting of 
two carbon rods, each about 8.83 inches in length, and 
Y 6 inch diameter, mounted vertically, side by side, on a 
base, at about 1 / 16 °f an inch apart, and insulated from 
each other by a composite substance, of which kaolin — 
porcelain clay — is the principal ingredient; which also 
forms an attachment between the carbons, and pro¬ 
duces the effect of the lime light as it consumes in 
connection with them. The candle thus formed is sup¬ 
ported on the base in a double spring clip through 
which the current enters, passing up one carbon and 
down the other, the upper extremities being connected 


THE ARC LAMP. 


191 

by a strip of graphite or other carbonaceous substance, 
which acts as a primer through which the current 
passes to establish the arc, and is consumed in the 
process, the current being subsequently maintained 
through the arc in the usual manner; hence if, 
through accident, the light becomes extinguished, it 
cannot renew itself. 

As equal consumption of the carbons is an absolute 
necessity with this candle, it can be used only with the 
alternating current. Each candle lasts about an hour 
and a half; and lamps are constructed containing several 
candles, and furnished with apparatus by which the 
cunent can be changed automatically from a burnt-out 
candle to a new one, each having a separate connecting 
wire ; while one common wire is used for the return 
current. Hence a lamp containing six candles furnishes 
light for nine hours. 

The required horse power on a circuit of five candles 
is 1.57 per candle, with ten candles 1.27, and with 
twenty candles .92; and the illumination of each light, 
without globe, 400 candle-power. It is evident that 
since the crater of the positive carbon, as well as the 
point of the negative, faces upwards, there must be, 
with this system, a great waste of light from direct 
upward radiation. The incessant variations of tint 
and brilliancy in the light, and the noise produced by 
the alternating current, has of late aided to bring this 
system, once so popular, into disrepute. 

The Jamin Electric Candle.— The loss of light 
from upward illumination with the Jablochkoff candle, 
and the lack of means for relighting automatically 
when accidentally extinguished, led to the invention of 
electric candles free from these defects, among which 


102 


THE ELEMENTS OF ELECTRIC LIGHTING. 


we find the Jamin candle, which is represented by 
Fig. 75. 

Two carbons, k k x , 1 / 6 inch diameter, are suspended 
point downwards, and surrounded below by a flat copper 


coil inclosed in a light case of copper foil, g g g g, 
which is attached to an insulating slate, p p, through 
which the carbons pass. The carbons are inclined at a 
slight angle so as to bring their points together, k being 

fixed, while k x is movable, and con¬ 
nected with a spring armature f by 
a pin s*, the armature being attached 
to the case below, and slightly sep¬ 
arated from it above. The coil is in¬ 
cluded in the electric circuit with the 
carbons; and when the current passes, 
the armature f is attracted, and kj 
separated from k by the pin s a suffi¬ 
cient distance to form the arc; the 
carbons, as consumed, being lowered 
by a wheel train inclosed in the tube 
shown above. Should the light be¬ 
come extinguished, the current being 
interrupted, the attraction of f ceases, 
and the retractile force of the spring brings the points 
of the carbons together, and renews the arc. A glass 
globe attached to p p incloses the lower part of the 
apparatus. 

A pair of carbons lasts about two hours ; and lamps 
are constructed with several pairs, and an arrangement 
by which, as each pair burns out, it consumes a fine 
brass wire which releases a spring by which the current 
is instantly changed automatically to the next pair; 
so that lamps constructed with three candles burn 



Fig. 75. 








THE ARC LAMP. 


193 


continuously for six hours without attendance. This 
candle, like the Jablochkoff, requires the alternating 
current. 

The Sun Lamp. — This lamp, invented by Clerc 
and Bureau, is illustrated by Fig. 76, and combines in 
its construction the arc and incandescent systems. To 
a metal frame g g is attached a block of marble or 
condensed magnesia, M M M, % to % inch thick, through 
which the carbons k k are transmitted, and by which 



Fig. 70. 


also they are insulated; the form of the opening through 
which they pass being so shaped that as they slide down 
by their own weight, or that of weights attached above, 
as they are consumed, they are prevented from passing 
through; their points entering a cavity in which the 
light is produced. 

They are attached above to the conductors d,d, insu¬ 
lated as shown, and connected with the electric circuit 
L, L. A primer, connecting the points of the carbons, 
establishes the arc; after which, current is maintained 
through the block, which becomes a conductor by being 













194 THE ELEMENTS OF ELECTRIC LIGHTING. 

heated between the carbon points. The arc is of 
exceptionally great length, varying from .39 ot an inch 
to 2.36 inches . while, in the ordinary arc lamp and 
Jablochkoff candle, it is only 1 / u to ] / s of an inch in 
length. The luminous point is fixed, and the light 
remarkably steady. It has a yellow tint when marble 
is used, and is of great intensity; the light being largely 
due to the incandescence of the lime formed from the 
marble, while the magnesia block produces a white 
light. Marble blocks last for two lighting periods of 
about ten hours each, the durability being reduced by 
the heating and cooling with shorter periods. The 
carbons vary in length from .two to twelve inches, 
and last about fifteen hours. 

The blocks vary in thickness, according to the re¬ 
quirements of the light, being made thinner for short 
circuits and strong currents than for long circuits and 
currents of less volume and greater intensity. Those 
made of condensed magnesia are more durable than 
those made of marble, being capable of lasting a hun¬ 
dred hours. 

The alternating current is preferred for this system, 
the lamp being closed to suppress the noise. The light 
is radiated downwards; but upward or horizontal radi¬ 
ation can also be obtained, springs being used to push 
the carbons. In another form of the lamp the carbons 
are placed horizontally, and have a special device for 
automatic relighting. The system is said to be eco¬ 
nomical, and the light, depending largely on the incan¬ 
descence of the marble or magnesia, but slightly affected, 
even by considerable variations of current strength. 

Automatic Adjustment of Arc Light Carbons. 
— The automatic adjustment of the carbons is the main 


THE ARC LAMP. 


105 


point in arc lamp construction, as upon this depends 
the production of the light, its renewal in case of ex¬ 
tinction, and, to a considerable extent, its constancy 
and steadiness. This adjustment, consisting in separa¬ 
tion and approach of the carbons, is operated and con¬ 
trolled by the electric current which creates the light, 
by various methods, as a train of clockwork, a break 
wheel or clutch operated by an electro-magnet, or a 
solenoid. The applications of these methods are nu¬ 
merous, and have led to the invention of a great 
number of different lamps. If the adjustment of the 
carbons in a single lamp were the only requirement, 
the problem would be comparatively easy; but the 
placing of a large number of lamps on one common 
circuit, and so regulating the resistance and the supply 
of current that each shall furnish an even, steady light, 
without interfering with the others, is a far more intri¬ 
cate and difficult affair. This regulation of a number 
of lamps on a common circuit is accomplished by the 
method originally proposed by Hefner von Alteneck, 
by which the regulating apparatus is placed in a shunt 
instead of in the main circuit; the shunt, which has a 
high resistance, causing the approach of the carbons, 
while their separation is produced by a coil of low 
resistance placed in the main circuit. 

The length of the arc is a very important matter. If 
too long, the intensity of the light, as well as its con¬ 
stancy and steadiness, is reduced, and the resistance 
abnormally increased. If too short, there is a decrease 
of intensity from insufficient resistance, and a wastage 
of the current from too great conductivity, the light 
obtained being less than the current can furnish. The 
length of the arc must also be adjusted to the amount 


THE ELEMENTS OF ELECTRIC LIGHTING. 


VMS 

of illumination for which the lamp is intended; and it 
is found, that, for lamps of 1,200 candle-power, the most 
practical length is about l / 16 of an inch; while, for those 
of 2,000 candle-power, it should be about 1 / s of an inch. 

The Foucault-Duboscq Lamp. —The first arc lamp 
with automatic regulation was invented by Foucault, 
and subsequently improved by Duboscq, and was con¬ 
structed with clockwork, operating by gearing; two 
vertical racks being connected with the carbon holders, 
and controlled by an electro-magnet and opposing spring 
in such a way, that, while the spring tended to bring 
the carbons together, the current which produced the 
light, passing through the electro-magnet, attracted an 
armature which tended to separate them, the carbons 
being placed vertically. The clockwork was operated 
by springs which required to be wound like those ot a 
clock. Either the constant or alternating current could 
be used, the feeding forward of the positive carbon 
being proportional to its increased consumption with 
the direct current. 

The Serrin-Lontin Lamp. — The construction of 
this lamp, invented by Serrin, and improved by Lontin, 
will be understood from Fig. 77. 

The carbons, not shown, are placed vertically in the 
usual manner, and connected above with the holders n 
and h x h 2 , the upper -f- carbon with n , and the lower — 
carbon with h 2 which moves vertically inside of h v 
A rack connected with n engages a gear wheel r to 
which is attached a wheel s, with which is connected a 
chain which passes over a pulley, and is attached to 
a support f, connected with the holder h 2 ; hence, as n 
descends by its weight, it raises h 2 , and the carbons 
approach each other. 


THE ARC LAMP. 


197 


A frame, a b c d , hinged at a and c, but having a 
free vertical motion at the side b d , is connected with 
the clockwork by the gear wheel r v and kept in equilib¬ 
rium by three spiral springs, two below and one above 
a transverse bar connecting it with the support t. A de¬ 
tent 2 , attached to this frame, releases the gear wheel r, 
permitting the motion of the 
clockwork, which brings the 
carbons together as de¬ 
scribed, in consequence of 
which a slight lowering 
of the frame occurs, and 
the detent z stops the clock¬ 
work. An electro-magnet 
£, placed in circuit with 
the carbons attracts an 
armature a , connected with 
the frame, when the current 
passes, drawing down the 
frame and the holder h. 2 
connected with it, separat¬ 
ing the carbons, and estab¬ 
lishing the arc. If the arc 
becomes abnormally long, 
the increased resistance 
reduces the current, and lessens the attraction of the 
armature, the springs raise the frame, pushing up the 
lower carbon, and the detent being at the same time 
released, the clockwork is put in motion, and the car¬ 
bons brought closer together. By this series of adjust¬ 
ments the arc is maintained at its normal length. By a 
screw Sj the pressure of the lower springs is so adjusted 
as to produce the requisite equilibrium. By a proper 


































198 THE ELEMENTS OF ELECTRIC LIGHTING 

adjustment of the gear wheel r and the wheel connected 
with it, the arc is adjusted to the required length. The 
current may be either direct or alternating. 

The Brush Arc-Light Lamp. — Among the numer¬ 
ous excellent arc-light lamps which have been con¬ 
structed, the Brush may be selected as an example of 
simplicity, and adaptation to the purpose for which it 
was designed. 

Fig. 78 is an ideal illustration of the construction, 
from which it will be seen that the adjustment of the 



carbons depends solely on the attraction of a solenoid, 
without the intervention of clockwork or gearing. 
X and Y are the terminals of the electric circuit, K 
and K' the carbons ; the lower carbon holder, connected 
with T, has a fixed position; while the upper holder, 
connected with AT, is free to move vertically. This 
movement is produced by the solenoids II, II , each of 
which is wound with coarse copper wire, and placed in 
the main circuit by connections at X and Y. At the 
right of X are shown three branches, one extending 



























the arc lamp. 


199 


to a resistance coil R; and the other two, after being 
coiled round the bobbins II, re-unite, as shown, and 
connect with the upper holder at N, the connection 
with Y being through the carbons K ’ K\ 

A shunt of fine copper wire, not shown in the cut, 
is connected directly with the terminals X and F, so 
that the current through it does not pass through the 
carbons. This shunt is coiled round the bobbins 
H, H , outside of the coarse wire, but in reverse order, 
so that the current passes through it in the opposite 
direction, thus partially neutralizing the magnetic effect 
of the current traversing the coarse wire. The shunt, 
having a high resistance, carries about one per cent of 
the entire current; but its coils being much more num¬ 
erous than the low resistance coils, their magnetic effect 
is proportionately increased. 

The carbons being in contact at the start, and the 
main current passing through them and through the 
low resistance coil, the cores of the solenoids are at¬ 
tracted, lifting the clutch (7, which grips the edge of 
the loose washer 7F, which being tilted at an angle, as 
shown, grips the upper holder, and lifts the carbon K , 
forming the arc. The separation of the carbons in¬ 
creases the resistance in the main circuit, and in like 
proportion the potential difference, or E. M. F., and 
hence the strength of the shunt current, which by 
its opposition to the main current reduces the magnetic 
attraction, and checks the ascent of the upper carbon 
when the arc has attained its normal length. A reduc¬ 
tion of resistance reverses these results, increasing the 
distance between the carbons. Thus, by the action of 
these opposing currents, the normal length of the arc 
is maintained; and this normal length may be adjusted 


200 


THE ELEMENTS OF ELECTRIC LIGHTING. 

as required, by varying the relative resistances of the 
two circuits when the lamp is constructed ; so that it 
can be maintained at one-sixteenth of an inch, one- 
eighth of an inch, or any other length required by the 
candle power of the lamp. If a lamp becomes acci¬ 
dentally extinguished, the relative change of resistance 
in the two circuits operates to bring the carbons together, 
and the light is instantly renewed. Sudden fluctuations 
in this series of adjustments, which would produce a 
flickering, unsteady light, are obviated by connecting 
the armature of the solenoid and the upper carbon 
holder with pistons moving in tubes filled with glyce¬ 
rine, by which smoothness and steadiness are imparted 
to the movements. 

Fig. 78 shows also a short-circuiting apparatus by 
which, in case of a lamp from any cause becoming per¬ 
manently extinguished, it is short-circuited, so that the 
How of current to other lamps on the same circuit is not 
interrupted. This apparatus consists of a resistance coil 
It, and an electro-magnet T, wound with coarse wire, 
placed in a direct open circuit between the terminals 
X and Y, as shown, through the hinged lever B and 
armature A. In addition to this open circuit, there is 
also a closed circuit of fine wire, wound on the bobbin 
T, in the same direction as the coarse wire, and forming 
part of the fine wire shunt of the solenoids II, H'. The 
ordinary current through this shunt, by which the lamp 
is regulated, is not sufficient to attract the armature A ; 
but if the lamp should happen to be permanently extin- 
guishedjthe resulting increase of current strength attracts 
A, and closes the coarse wire circuit through the contacts 
M, M', so that the main current flows past the extin¬ 
guished lamp to the other lamps on the same circuit. 


THE ARC LAMP . 


201 


By adapting the resistance of R, and the windings of the 
bobbin T, to the strength of tlie current, the requisite 
adjustment can be obtained. 

I he carbons, twelve inches long, last about eight 
hours, about three-fourths of the positive carbon and 
one-third of the negative being consumed. The lamps 
are usually constructed with either one or two pairs of 
carbons, but can be made with three or more pairs if 
necessary; and, by the simple device shown in Fig. 79, 
each pair is lighted in succession automatically when 
the pair previously lighted has burnt out. The frame 



Fig. 79. 


K\ which is connected with the solenoids, is adapted to 
two pairs of carbons. The clutch on the left is narrower 
than the one on the right; it consequently grips the 
washer W 1 and lifts the carbon-holder R l before the 
right clutch can grip W 2 and lift R 2 ; the current, which 
at first passes equally through both pairs of carbons, is 
now, in consequence of the separation of the left pair, 
diverted through the right pair alone; the frame con¬ 
tinues to rise, the right pair are separated and the arc 
established. 

The separation of the left pair is too great to admit of 
the formation of the arc ; but when the right pair is so 
































202 


THE ELEMENTS OF ELECTRIC LIGHTING. 


far consumed that the light is extinguished, and they 
can no longer be brought together for relighting, the 
left pair is brought into contact, and the arc re-estab¬ 
lished automatically, less than a second being required 



to renew the light. Fig. 80 represents a single lamp, 
and Fig. 81 a double lamp ; the controlling and regu¬ 
lating apparatus being inclosed in the circular case 
above the carbons. 



























































THE ARC LAMH 


203 


The solenoid and clutch method of automatic regula¬ 
tion, variously modified, is now employed in numerous 
arc lamps besides the Brush; the method with clock¬ 
work, or gearing, is also in common use; and the two 
methods are also sometimes combined. 

In the consumption of arc-light carbons, cones of half 
to five-eighths of an inch in length are maintained on 
both carbons, that of the lower carbon being pointed, 
while that of the upper carbon is truncated, the crater 
occupying about one-third of the diameter. As these 
cones are incandescent, light is radiated from a space, 
including the arc, of an inch or more in length, while 
the actual distance to which the carbons are separated 
is only one-sixteenth to one-eighth of an inch: the in¬ 
candescence of the upper -f- carbon is more intense, and 
yields much more light, than that of the lower — carbon. 

The Inclosed Arc Lamp. —This lamp, which came 
into commercial use in 1895-6, differs from the lamps 
already described by having its arc inclosed in a glass 
bulb about the size of a small lamp chimney, and usually 
of similar shape, its central diameter being about twice 
the average diameter of its ends; it is also made cylindric 
in shape. It is usually opalescent, but sometimes trans¬ 
parent; and is inclosed in a large, opalescent globe, 
which may be open, or nearly closed if the lamp is in¬ 
tended for outdoor use. 

This bulb is nearly air-tight, being closed below by 
the lower carbon-holder, and above by a close-fitting 
metal cap through which the upper carbon passes; the 
only opening being a limited space around this carbon, 
sufficient to allow its vertical movement without friction. 
Hence the carbons burn in partly deoxidized air, charged 
with carbonic dioxide, and consequently at a very slow 
rate of combustion, their average durability being about 


204 


T1IK ELEMENTS OF ELECTRIC LIGHTING. 


125 hours, or fifteen times as long as that of the open 
are carbons. 

The regulating apparatus is similar to that in other arc 
lamps, the upper carbon being moved by a solenoid and 
clutch. The supply of current is regulated by a resist¬ 
ance coil, usually placed in the upper part of the lamp, 
but sometimes at some other conveniently accessible point 
in the circuit. The volume of current is about five 
amperes, which is about half that employed in open arc 
lamps, and the E. M. F. is about 80 volts, or nearly 
twice that in open arc lamps. As a result of this, the 
inclosed arc is thinner and much longer than the open 
arc, and gives nearly an equal quantity of light, of 
clearer quality. Its average length is four to five times 
the average length of the open arc. Ilence the shadows 
of the carbon points, which interfere seriously with the 
radiation of the light from the open arc, are scarcely per¬ 
ceptible with this arc; and these points, instead of being 
cone-shaped, with a crater in the upper point, burn 
nearly fiat, without a crater. 

The carbon dust is entirely consumed in this lamp, 
and the formation and escape of sparks is prevented; 
hence it is much cleaner for indoor use than the open arc 
lamp, and involves no increase of lire risk and conse¬ 
quent rate of insurance. The cost of carbons is about 
one-fifteenth that for the open arc lamp, and the cost of 
attendance about one-tliird, daily trimming and renewal 
of carbons not being required. This amounts to an 
annual saving of $12 to $15 per lamp, a very material 
item where a number of lamps are in use, as in a large 
store, besides the saving of inconvenience and annoyance 
caused by the lamp trimmer’s daily visit. The light is 
steadier and more uniform in distribution than that of 


THE ARC LAMI\ 


205 


the open arc lamp, and there is no flush and consequent 
waste of current when the lamp is lighted. 

These lamps are intended chiefly for indoor use, but 
can also he employed for street lighting, and may event¬ 
ually supersede the open arc lamps for both purposes, 
when their superior advantages are fully realized. They 
can he used with either the series or parallel systems 
of distribution described in chapter X, though ‘chieflv 
intended tor the latter, and on the same circuit with 
open arc lamps, or incandescent lamps. 


CHAPTER VIII. 


The Incandescent Lamp. 

Whide the arc lamp is well adapted for lighting large 
areas requiring a powerful, diffused light, similar to 
sunlight, and hence is suitable for outdoor illumination, 
and for workshops, stores, public buildings, and facto¬ 
ries, especially those where colored fabrics are pro¬ 
duced, its use in ordinary dwellings, or for a desk light 
in offices, is impractical, a softer, steadier, and more 
economical light being required. Various attempts to 
modify the arc-light by combining it with the incandes¬ 
cent were made in the earlier stages of electric lighting, 
among which was the sun lamp already described; 
besides this, Reynier’s lamp, invented in 1877, was the 
most successful. Its construction is briefly as fol¬ 
lows : — 

Reynier’s Lamp. — A carbon rod impinges on the 
circumference of a circular block of carbon which has 
a rotary motion on its axis. The rod, 12 inches long 
and Y 12 °f an inch in diameter, is attached by a horizon¬ 
tal support above to a brass holder which has a free 
vertical motion in a brass tube placed on a level with 
the carbon block, and by its weight keeps the rod as it 
is consumed in contact with the block. The rod is 
guided in its descent between a small copper roller on 
one side and a short pointed carbon on the other, the 
current entering the rod through this point at about 


THE INCANDESCENT LAMP. 


207 


l U of an * nc h above its contact with the carbon block, so 
that this short portion becomes incandescent, and pro¬ 
duces the light. A brake connected with the carbon- 
holder and block by a horizontal support regulates 
the descent of the carbon rod; and the rotation of the 
block, produced by the pressure of the rod as it de¬ 
scends and is consumed, removes the ash and slag. A 
rod lasts about two hours, and furnishes a light of 114 
to 150 candle-power. But the ratio of light produced 
to electric energy consumed does not exceed J / 6 of that 
produced by the arc light, and the carbon rod is liable 
to break and extinguish the lamp. 

Various improvements in this lamp have been 
attempted, such as the substitution of a copper block 
for the carbon block, also of shorter and thicker rods, 
less liable to fracture, and of several rods lighted auto¬ 
matically in succession, also of springs or clockwork for 
gravity in maintaining the contact of the carbons ; but 
none of these semi-incandescent lamps have come into 
general practical use, though their efficiency in propor¬ 
tion to electric energy consumed was greatly increased 
above that of the Reynier lamp, so that an efficiency 
three times as great in proportion to consumption of 
energy as that of the strictly incandescent lamp, is said 
to have been attained ; and it is possible that such effi¬ 
ciency may ultimately be attained as to bring this 
system into general use. 

Early Experiments. — The first strictly incandes¬ 
cent lamp was invented in 1841 by Frederick de 
Molyens of Cheltenham, England, and was constructed 
on the simple principle of the incandescence produced 
by the high resistance of a platinum wire to the pas¬ 
sage of the electric current. In 1849 Petrie employed 


208 


THE ELEMENTS OF ELECTRIC LIGHTING . 


iridium for the same purpose, also alloys of iridium and 
platinum, and iridium and carbon. In 1845 J. W. 
Starr of Cincinnati first proposed the use of carbon, 
and, associated with King, his English agent, produced, 
through the financial aid of the philanthropist Peabody, 
an incandescent lamp having twenty-six lights, which 
attracted the attention and excited the admiration of 
Faraday. The advantages of carbon over platinum 
consist in its greater electrical resistance, which is 
two hundred and fifty times that of platinum ; its 
absolute infusibility, even at very high temperatures; 
its lower thermal capacity, by which the same amount 
of heat produces a much higher temperature ; and its 
greater illuminating power at the same temperature as 
platinum. 

In all these early experiments, the battery was the 
source of electric supply; and the comparatively small 
current required for the incandescent light as compared 
with that required for the arc light, was an argument in 
favor of the former; twelve Bunsen elements being suf¬ 
ficient to produce twelve incandescent lights in one cir¬ 
cuit, as demonstrated by DeChangy of Paris, in 1857, 
while twenty-four to forty elements were required to 
produce a single arc light. Still, no substantial prog¬ 
ress was made witli either system till the invention of 
the dynamo resulted in the practical development of 
both systems, that of the incandescent following that 
of the arc. 

Among the first to make incandescent lighting a 
practical success were Sawyer & Man of New York, 
and Edison. For a long time, Edison experimented 
with platinum, using fine platinum wire coiled into a 
spiral, so as to concentrate the heat, and produce 


TIIE INCANDESCENT LAMP. 


209 

incandescence; the same current producing only a red 
heat when the wire, whether of platinum or other 
metal, is stretched out. A metal rod, placed inside the 
coil, was so arranged that when the temperature 
approached the point where the coil was liable to 
fusion, the expansion of the rod closed a short circuit, 
which reduced the current strength, and consequently the 
temperature: the contraction of the rod produced by the 
cooling, opened this circuit, and increased incandescence 
followed. 

Failing to obtain satisfactory results from platinum, 
Edison turned his attention to carbon, the superiority 
of which as an incandescent illuminant had already 
been demonstrated : but its rapid consumption, as shown 
by the Reynier and similar lamps, being unfavorable to 
its use as compared with the durability of platinum 
and iridium, the problem was, to secure the superior 
illumination of the carbon, and reduce or prevent its 
consumption. As this consumption was due chiefly to 
oxidation, it was questionable whether the superior 
illumination were not due to the same cause, and 
whether, if the carbon were inclosed in a glass globe, 
from which oxygen was eliminated, the same illumina¬ 
tion could be obtained. Another difficulty of equal 
magnitude was to obtain a sufficiently perfect vacuum, 
and maintain it in a hermetically sealed globe inclosing 
the carbon, and at the same time maintain electric con¬ 
nection with the generator through the glass by a 
metal conductor, subject to expansion and contraction 
different from that of the glass, by the change of 
temperature due to the passage of the electric current. 
Sawyer A Man attempted to solve this problem by filling 
the globe with nitrogen, thus preventing combustion by 


210 THE ELEMENTS OF ELECTRIC LIGHTING 

eliminating the oxygen, and at the same time maintain¬ 
ing a pressure equal to that of the external atmosphere, 
so that the leakage by the expansion and contraction 
of the metallic conductor would be insignificant. 

The results obtained by this method, which at one 
time attracted a great deal of attention, were not suf¬ 
ficiently satisfactory to become practical; and Edison 
and others gave their preference to the vacuum method, 
and sought to overcome the difficulties connected with 
it. The invention of the mercurial air pump, with its 
subsequent improvements, made it possible to obtain a 
sufficiently perfect vacuum, and the difficulty of intro¬ 
ducing the current into the interior of the globe was 
overcome by imbedding a fine platinum wire in the 
glass, connecting the inclosed carbon with the external 
circuit; the expansion and contraction of the platinum 
not differing sufficiently from that of the glass, in so 
fine a wire, as to impair the vacuum. 

Incandescent-Light Carbons. — The next point 
of greatest importance was to obtain carbons of the 
proper consistence, tenacity, and durability; and this, 
as in the case of arc-light carbons, required a long series 
of delicate and costly experiments with a variety of 
materials, treated by a variety of different processes. 

The Edison Carbons. — The carbons made by 
Edison under his first patent in 1879, were obtained 
from brown paper or cardboard, cut into narrow strips 
in the form of a horse-shoe, which was about 2 l / 4 inches 
long, and l l / 2 inch in diameter. These were reduced 
to carbon in an iron mold placed in a muffle, and 
maintained at a high temperature. They were very 
fragile and short-lived, and consequently were soon 
abandoned. In 1880 he patented the process which, 


THE INCANDESCENT LAMP. 


211 


with some modifications, he still adheres to. In this 
process he uses filaments of bamboo, which are taken 
from the interior, fibrous portion of the plant. The 
cane, after being cut into sections of the required 
length, and the hard outer surface removed, is split and 
shaved down into flat strips, which are then pressed 
between dies, and fine filaments of the required length 
and diameter obtained. These are placed in molds 
made of nickel, in grooves of the required horse-shoe 
form, and closed so as to exclude the air. The molds 
are then placed in muffles, and the filaments carbonized 
at a very high temperature. They are then attached 
to their platinum wire supports by electro-copper¬ 
plating, and introduced into the little lamp globes. 
The lamp is then attached to a Sprengel airpump, and 
during the process of exhaustion the filament is alter¬ 
nately heated and cooled by an electric current; the 
temperature being gradually raised by increase of cur¬ 
rent strength after each cooling, till a high degree of in¬ 
candescence is attained. This removes all the occluded 
gases which remain after the carbonizing, and renders the 
carbon homogeneous, elastic, and refractory at a high 
degree of temperature. As this is a far more severe 
test than any to which the carbon will be subjected in 
use, all imperfect and defective carbons are destroyed 
in the process, and only the best survive. 

The Lane-Fox Carbons. — In the manufacture of 
the Lane-Fox carbons the raw material is obtained 
from the bass broom, a species of grass fiber. The 
hard outer surface is removed by immersion in a solu¬ 
tion of hot caustic soda or potash, and subsequent 
scraping, after which the alkali is removed with boiling 
water, and the fibers, in lots of about a hundred, 


212 


THE ELEMENTS OF ELECTRIC LIGHTING. 


bound to blocks of plumbago, shaped so as to give them 
the horse-shoe form. These blocks, in lots of fifty, are 
imbedded in powdered charcoal in graphite crucibles, 
placed in a furnace, and subjected for twenty minutes 
to a white heat. The fibers, after being carbonized in 
this manner, are gauged and sorted, and all of the same 
diameter placed together, after which they are sus¬ 
pended separately from spring clips by attachment at 
the ends, in large globes filled with a hydrocarbon gas 
obtained from benzole or coal, and subjected to the 
process termed flashing, first proposed by Sawyer. 
This process consists in rendering the filaments incan¬ 
descent, either by the passage of an electric current, or 
by the heat of a furnace, the latter being the method 
adopted in the Lane-Fox process. The gas in contact 
with each filament being decomposed, a layer of hard 
carbon is deposited, which renders the filament denser, 
smoother, more homogeneous, more durable, and more 
uniform in size ; the smaller parts becoming hotter than 
the larger, and thus acquiring a thicker deposit. The 
increased diameter reduces the resistance, and the pro¬ 
cess is continued till the resistance required for lamps 
of a given candle-power, ranging from sixteen to sixty, 
is obtained. 

The Cruto Carbons. — These are made by using 
as a base a fine platinum wire bent into the horse-shoe 
form, upon which the carbon is deposited by the flash¬ 
ing process. This is effected by attaching the wires, 
placed in a long glass vessel, to insulated metallic sup¬ 
ports, by which an electric current can be sent through 
each of them. A current of olefiant gas, C 2 I ^circu¬ 
lates through this vessel, the gas being made from 
alcohol and sulphuric acid, purified by passing through 


THE INCANDESCENT LAMP. 


213 


water and lime water, and dried by calcium chloride 
and sulphuric acid, thus furnishing a gas of pure hydro¬ 
carbon. The platinum wires are connected with a 
shunt circuit so that an electric current passing through 
them can be graduated to any required strength by a 
resistance varying from one ohm to two hundred ohms. 
The wire being heated to incandescence in this manner, 
the gas is decomposed, and carbon deposited. To 
insure a uniform deposit, it is necessary to guard against 
the influence of the earth’s magnetism by placing the 
wires in a plane at right angles to that indicated by 
the dip of the magnetic needle; and in the latter part 
of the process the current is reversed. This operation, 
which requires about two and a half hours, produces a 
filament remarkably compact and homogeneous, and 
uniform in cross-section and resistance. Special care is 
required to maintain uniformity in the successive stages 
of the process, otherwise the result is a filament of dis¬ 
similar superimposed layers of carbon, lacking homo¬ 
geneity, and practically worthless. 

The Swan Carbons. — These carbons are made 
from cotton twine, prepared by immersion in sulphuric 
acid diluted with one-third part water, by which they 
attain a consistence similar to that of parchment; they 
are then thoroughly washed to remove the acid, reduced 
to a uniform cross-section by being passed through 
discs, after which they are wound on rods of carbon or 
earthen ware, each in the form of a flat spiral having 
one convolution, and carbonized by being imbedded in 
powdered charcoal in a crucible raised to a white heat. 
They are subsequently coated with carbon by the flash¬ 
ing process, and, like the Edison carbons, heated and 
cooled alternately by the electric current to remove 


214 THE ELEMENTS OE ELECTRIC LIGHTING. 

the occluded gases, while inclosed in the globe during 
its exhaustion. Each filament, when finished, is 5 inches 
long and .005 of an inch in diameter. 

The Weston Carbons. — The raw material used 
for these carbons is cotton or linen cellulose, which by 
the action of nitric and sulphuric acids is converted into 
nitro-cellulose — gun cotton — which is subsequently 

dissolved in a mixture of alcohol 
and ether and converted into col¬ 
lodion, and finally has its combus¬ 
tibility reduced by the action of 
ammonium hydrosulphide or other 
chemical agent producing a similar 
effect. 

This artificial product, which 
Weston calls “ Tamadine,” is an 
amber-colored, amorphous cellulose 
of great ductility, tenacity, and 
homogeneousness. It is rolled into 
thin sheets between steel rollers, 
and filaments of the sizes required 
for lamps of different candle-power 
are cut from the edge of the sheet, 
bent on shapes into the horse-shoe 
form, carbonized in the usual manner, 
and flashed in hydrocarbon gas by the electric process. 
The carbons when finished are highly elastic, and have 
a smooth brilliant surface like that of a steel watch- 
spring. 

The Bernstein Carbons. — These are made from 
silk ribbon of the finest texture, woven into a hollow 
cylinder of the required size, from which sections of the 
proper length are cut, which are immersed in a thick 













THE INCANDESCENT LAMP. 


215 


syrup of cane sugar till saturated, and subsequently in 
melted paraffine; they are then bent on shapes into the 
horse-shoe form, placed in graphite molds of the same 
shape and imbedded in graphite powder, and baked for 
twenty-four hours. The subsequent flashing process is 
the same as that for the Lane-Fox carbons. This fila- 



Fig. 83. 


ment showing the woven structure, is illustrated by Fig. 
82, and two of the lamps by Fig. 83, one with a short 
filament, giving it low resistance, and the other with a 
long filament, giving it high resistance. 

These are the only carbons made from an animal 
substance, and with a hollow structure ; and the advan¬ 
tage claimed for this structure is increase of suiface, 



























































THE ELEMENTS OF ELECTRIC LIGHTING. 


216 


and consequently of radiating capacity with a given 
degree of resistance. 

General Details of Filament Construction. 
— More or less of the details of the various processes 
of manufacture are trade secrets, as in the case of arc- 
light carbons ; and in some instances the whole process 
is kept secret, as in the manufacture of the Siemens- 
Halske and also of the Woodhouse-Rawson carbons. 

As the length and diameter of the filament determines 
to a great extent its electric resistance and illuminating 
power, it varies according to the E. M. F., current, and 
kind of carbon employed, so that exact figures can not 
be given. The Swan filament, as we have seen, is about 
5 inches long and .005 of an inch in diameter, and may 
be taken as representing approximately the average 
dimensions required for the ordinary 16 candle-power 
lamp. 

The shape of the filament varies, the horse-shoe form 
being the most common; the Swan filament, adopted 
also for the Brush lamp, is a flat spiral, as already 
mentioned, while the Maxim resembles a capital M 
with the angles rounded off. The Sawyer-Man filament 
resembles a figure 8. Fig. 84 shows an Edison lamp, 
and Fig. 85 a Weston, both with horse-shoe filaments; 
and Fig. 86 a Weston witli corrugated filament. 

The cross-section of the filament is also a point of 
considerable importance, determining not only its 
strength in resisting jars, concussion, and high temper¬ 
ature, but also its illuminating power. As the rectan¬ 
gular form gives greater surface than the circular with 
the same cross-section, the illumination with a given 
length is greater, but mis can oe compensated in the 
circular form by increasing the length; this increases 


THE INCANDESCENT LAMP . 


217 



Fig. 81 

















































































































218 


THE ELEMENTS OF ELECTRIC LIGHTING 


the resistance, and consequently the E. M. F. without 
increase of current. Hence the same illumination can 
he obtained from the round filament as from the rect¬ 
angular with greater economy of current. The hollow 
•circular filament, like the Bernstein, gives the maxi¬ 



mum of surface with the minimum of substance in 
cross-section, and hence, as we have seen, the maximum 
of illumination with the minimum of resistance, and 
also the maximum of strength in proportion to sub¬ 
stance and resistance. Hence, if reduction of resist¬ 
ance in proportion to strength and illumination is 




































































the incandescent lamp. 


219 


clesii eel, either tlie rectangular or the hollow circuhir 


form is preferable; but if increased resist 
portion to strength and illumination is 


ance in pro- 
desired, the 


solid circular form with increased length is preferable. 

The filament is in all cases made largest at the points 
of attachment, either in the form given previous to 


carbonizing, or by the subsequent deposition of carbon 


on the extremities, or their insertion into small perfo¬ 
rated carbon cylinders. This is necessary for the pur¬ 
pose of better attachment to the platinum wires, but 


more especially to reduce the resistance, and hence the 
strain on the filament at the points where the current 
enters and leaves, and to increase the strength where 
liability to fracture is greatest. The attachment of 


the filament to the platinum wires is accomplished by 
different methods; that of the Edison, by copper plat¬ 
ing, has been already mentioned. The Lane-Fox fila¬ 
ments are cemented into short carbon cylinders, to 
which also the platinum wires are similarly attached 
with a cement made of India ink and plumbago. The 
attachment of the Cruto filaments is effected by their 
insertion into tubes formed on the ends of the platinum 
wires, and the subsequent deposition of carbon by the 
electric process on these junctions. The Weston fila¬ 
ment terminates in carbon cylinders, nickel plated, each 
about 3 /ie °f au inch in length and y 32 of an inch in 
diameter, around which are wound in spirals the 
flattened extremities of the platinum wires. This 
method is also used with the Bernstein filaments, and 
is attributed to W. Siemens. 

The average durability of filaments is estimated at 
from 600 to 1,000 hours, or from 2 % to 4 months, 
with an average use of from eight to nine hours a 


220 THE ELEMENTS OF ELECTRIC LIGHTING. 

day. While there is no actual consumption such as 
occurs with arc-light carbons, there' is a certain amount 
of wastage caused by the incandescence and residual air, 
infinitesimal particles of carbon being given off, in the 
form of vapor, and being attracted to the glass in con¬ 
sequence of the difference of potential between it and 
the filament, adhere to the sides of the globes, producing 

a certain degree of blackening. 

It has been observed by Edison that with the direct 
current this wastage is greater in one half of the 
filament than in the other. this may be accounted 
for by comparing the positive and negative halves of 
the filament to the positive and negative carbons of an 
arc-light pair; and since the consumption of the posi¬ 
tive carbon by its electric conversion into vapor is far 
in excess of that of the negative, the same process, 
which we may reasonably assume occurs in the filament 
on a very limited scale, and proceeds from the same 
* cause, will account for this unequal wastage. It is 
also well known that the durability of the filament is in 
proportion to the perfection of the vacuum, the residual 
air producing slight oxidation during incandescence, 
which, as in the arc light, would be greatest on the 
positive side. 

But, besides the reduction from wastage, the intense 
molecular action during incandescence, the alternate 
heating and cooling, and probably also a certain species 
of electrolysis, which has been observed in solids as in 
liquids, reduce the structural tenacity, and are the chief 
causes which eventually result in the rupture of the 
filament. This is further shown by the fact that its 
durability depends largely on the amount of current 
employed. Increased current produces increased light, 


THE INCANDESCENT LAMP. 


221 


but shortens the durability, and it becomes an impor¬ 
tant economic problem to determine just what amount 
of current to employ with filaments of a given size 
and resistance, especially as the rupture of the fila¬ 
ment practically terminates the life of the lamp, since 
filaments cannot, like arc-light carbons, be replaced 
with new ones in the same lamp, on account of the 
hermetical sealing and exhaustion of the globe. 

Since the wasting of the filament results not only in 
the conversion of luminous carbon to the black deposit 
which obstructs the light, but also in increase of resist¬ 
ance by reduction of the filament’s cross-section, and con¬ 
sequent decrease of current strength, and hence of illu¬ 
mination at the same potential, the practical value of the 
lamp usually ceases long before the rupture of the 
filament, and its further use ceases to be economical. 

Lamps of high illuminating power, 100 to 200 candle- 
power, are constructed either with filaments of propor¬ 
tionally increased cross-section, or with two or more 
filaments connected in parallel. In the latter construc¬ 
tion, the rupture of a filament, though proportionally 
reducing the light, does not extinguish the lamp, as in 
the single filament construction. Lamps of 16 to 32 
candle-power, for railway service, are also sometimes com 
structed with two short filaments connected in series, the 
length of each, and the risk of filament rupture by the 
jarring of the cars being thus proportionally reduced 
without reduction of resistance. 

Taking three of the leading incandescent systems, as 
fairly representing the best practical experience in this 
method of electric lighting, we find that the E. M. F. of 
the ordinary 16 candle-power lamp ranges from 52 volts 
to 115, and its current strength from .46 of an ampere to 


THE ELEMENTS OF ELECTRIC! LIGHTING. 


9 , 99 , 


1.04; the averages being 90.82 volts, and .65 of an 
ampere, which gives 3.69 watts per candle-power as the 
average consumption of electric energy. It is found that 
the flashed filaments are the most durable, and give, on 
an average, a third more light than those not so treated. 



Construction of the Incandescent Lamp. — As 
the main features of the incandescent lamps are very 
similar, we may take the latest Weston 16 candle-lamp, 

































































THE INCANDESCENT LAMP. 223 

Figs. 85 and 86, as a fair sample of their construction. 
The glass globe, or bulb, is about 3 1 / 2 inches long by 
2 V 4 inches in diameter. The filament of the horse¬ 
shoe form is attached to the platinum wires, as already 
described; and these pass through two little tubes, as 
shown in Fig. 87, at the inner closed end of a hollow 
glass stopper fitted to the neck of the bulb, the glass 
being fused round them. The neck is wide enough to 
admit the filament into the bulb without compression ; 
and, after its introduction, the glass is fused around the 
stopper. A short glass tube projects from the broad 
end of the bulb, through which the air is exhausted 
from the interior; after which it is fused, thus sealing 
the globe hermetically. 

The outer end of the tubular stopper is fitted with a 
wooden insulating plug, which has a central projection 
about three-eighths of an inch long and one-fourth of 
an inch in diameter, through which a copper wire, con¬ 
nected with one of the platinum wires, passes, and is 
attached to a brass screw at its outer extremity; while 
a copper wire from the other platinum wire connects 
with a metal washer attached to the broad part of the 
plug, so that the wires are insulated from each other. 
A brass collar, connected to the neck outside, fits into a 
brass tube about two inches long and one inch in diam¬ 
eter, connected to the bracket or chandelier. In this 
tube are two metal springs, — one of which terminates 
in a washer, which slips over the projection of the insu¬ 
lating plug, and makes contact with the metal washer 
on the broad part; while the other makes contact with 
the screw at the extremity of the projection. These 
springs are insulated from each other, and connected 
with the electric circuit, so that the current from one 


224 THE ELEMENTS OF ELECTRIC LIGHTING. 


must pass through the filament to reach the other. 
The circuit is opened and closed by a hinged metal con¬ 
tact piece, operated by an insulating handle ; the clos¬ 
ing being effected by the pressure of this piece against 
a pair of springs so connected with the springs already * 
mentioned as to complete the circuit, and the opening 
by a reverse turn of the handle, which breaks the con¬ 
tact, so that the lamp is lighted or extinguished by a 
quarter turn of the insulating handle, like a gas jet. A 
lozenge-shaped piece of metal attached to the handle, as 
shown, presses down the hinged contact piece to close 
the circuit, and holds it in position, and a spiral spring 
lifts it when released, and opens the circuit, the whole 
apparatus being inclosed in the brass tube mentioned 
above. 

The lamp bulb is held in connection with this tube, 
and inclosed apparatus, by little projections on the brass 
collar attached to its neck, which slip into a groove 
in the lower end of the tube; so that when a filament 
breaks, it is but the work of a moment to remove the 
defective bulb and replace it by a new one, the only 
loss being the bulb and filament, the other apparatus 
remaining permanent, and the connections with the 
new bulb taking place by contact, without further 
manipulation, as soon as it is placed in position. 

It will be seen from Figs. 88 and 89, which represent 
different styles of the latest Swan lamp, that the method 
of mounting the lamp, and connecting it with the elec¬ 
tric circuit, is essentially the same as that of the Weston 
and Edison, as shown by the description and illustra¬ 
tions already given ; the bulb with its inclosed filament, 
platinum wires and connections, and brass collar, form¬ 
ing one part; and the brass tube to which it is attached, 



J?ig. 33. 





























































226 


THE ELEMENTS OF ELECTRIC LIGHTING. 



Fig. 89. 

























































































































































THE INCANDESCENT LAMP. 


227 


as shown, containing the apparatus for opening and 
closing the circuit by an insulating handle, forming the 
other part. This apparatus may be varied indefinitely, 
its construction being a mere matter of mechanical detail. 

Position of Lamp. —This lamp does not require a ver¬ 
tical position, like the arc lamp, but may be placed in any 
position most convenient for the radiation of the light. 

Vacuum Tube Lighting. —This method of electric 
lighting is still in the experimental stage, but promises 
in the near future to come into practical use, and may 
eventually supersede incandescent lighting. The light 
is generated by electric action producing molecular move¬ 
ment in the residual air contained in glass tubes or bulbs, 
without interior filaments or electrodes, in which a high 
vacuum has been produced. Three different methods 
have been devised, by Tesla, Edison, and Moore, respect¬ 
ively. 

Tesla uses an ordinary lamp bulb with platinum wires 
sealed into the neck, and connects it with an induction 
coil of special construction, operated by an alternating 
current of very high E. M. F., made disruptive by a 
toothed wheel interrupter. The light may also be pro 
duced by bringing this lamp within the inductive influ¬ 
ence of the coil, without direct connection. 

Edison uses a tube having platinum wires sealed into 
its ends and coated inside with a special fluorescent 
material which does not disintegrate and thus reduce the 
vacuum. This tube when connected with an induction 
coil traversed by a rapidly intermittent electric current, 
is lighted by a fluorescent effect produced on this inner 
coating by the residual air. 

Moore uses a long tube which may lie folded into any 
compact, ornamental form, and coats the ends and a cen- 


228 


Tilt1 ELEMENTS OE ELECTRIC LIGHTING. 


tral space externally with metallic paint, on which are 
wrapped wire terminals. The central terminal is con¬ 
nected with a source of low potential current, and the 
end terminals with one of high potential current which 
traverses a primary coil and is made intermittent by a 
vibrator of special construction. 

This vibrator is inclosed, with its contact points, in a 
glass tube of high vacuum, under which is placed the 
attracting electromagnet which operates it. Hence the 
spark which occurs at break, at the contact points of an 
ordinary vibrator, and is caused by the resistance of the 
air traversed by a portion of the current, is suppressed 
by the absence of air in this tube, and the consequent 
complete intermission of the current; and the electric 
energy which would he wasted by the spark is applied to 
the production of the light. There is also a saving of 
electric energy in the employment of a primary coil in 
preference to an induction coil *, so that the energy 
required for this lamp does not exceed that employed in 
the ordinary incandescent lamp. 

The end terminals are of equal area and potential, and 
may he of the same polarity or of opposite polarities, and 
the central terminal may be of either polarity; difference 
of polarity being apparently of no importance, while 
difference of potential between the central and end term¬ 
inals is of the highest importance. 

In each of these lamps, the whole interior glows with 
a white, phosphorescent light, having but little heat*, 
and the lamps, being without filaments or interior elec¬ 
trodes of any kind, are practically indestructible. So 
that the long sought desideratum of an indestructible 
lamp, giving light without heat, seems about to be real¬ 
ized. 


CHAPTER IX. 


The Storage Battery. 

Electric Storage. — When water is . decomposed 
by an electric current, and the gases collected in sepa¬ 
rate receptacles, if the connection with the battery be 
severed, and the wires leading to the gas tubes brought 
into contact, a current of electricity will flow through 
them in the reverse order to that of the original cur¬ 
rent, the gases at the same time recombining to form 
water. From which it is evident that the electric 
energy expended in decomposing the water is stored 
up in the gases, and recovered when they recombine. 
Oxygen accumulates at the positive pole, and hydrogen 
at the negative; and in order to collect the gases, 
platinum terminals for the wires are required, since 
the oxygen unites with the terminal, if composed of 
any of the baser metals, and appears in the combined 
form of an oxide instead of the separate form of a gas. 
But experiment proves that electric energy is also 
stored up in the oxide when so formed, and may be 
recovered from it. 

Observation of these facts by Gautherot and Bitter 
in the early part of the present century, indicated the 
possibility of storing electricity so as to obtain a con¬ 
tinued current similar to that from the battery, instead 
of the instantaneous discharge obtainable from the 
Leyden jar, or the condenser. On this principle Grove, 


230 THE ELEMENTS OF ELECTRIC LIGHTING. 


in 1842, constructed a gas battery, using at first oxygen 
and hydrogen collected in glass tubes with platinum 
electrodes*, but subsequently various other gases, and 
finally plates covered with peroxides of metals. Nu¬ 
merous other attempts to accomplish this were made 
from time to time by Wheatstone, Siemens, Kirchoff, 
and others, but without any practical result till about 
1859, when Gaston Plante, a French electrician, began 
a course of experiments for this purpose, which resulted 
in the discovery that lead plates could be so prepared, 
electrically, as to produce the desired result, by allow¬ 
ing the ox}^gen, as it accumulates at the positive pole, 
to combine with the lead of a plate provided for 
that purpose, and form a peroxide (Pb0 2 ), while the 
hydrogen accumulates on a similar plate at the nega¬ 
tive pole. And on this principle lie constructed his 
secondary cell. 

Plante’s Secondary Cell. — This cell was origi¬ 
nally constructed with two plates of sheet lead, sepa¬ 
rated by strips of gutta-percha one sheet being laid 
over the other with two gutta-percha strips between 
them, and two more laid on the upper sheet, as shown 
at A, Fig. 90. They were then rolled together and 
clamped, giving them the compact form shown at J5, 
a strip of lead being left attached to one corner of each 
sheet in cutting, by which connection could be made 
for charging and discharging. The sheets, rolled to¬ 
gether in this manner, were placed in a tall jar of glass 
or hard rubber, containing water mixed with ten per cent 
of sulphuric acid ; the jar being fitted with a hard-rubber 
cover provided with binding screws, to which the con¬ 
necting strips were attached, and also clamps for hold 
ing wires to show the heating effects of the discharge. 


THE STORAGE BATTERY. 


231 


I lie next step was the electrical preparation of the 
plates, which was accomplished by charging them with 
a battery of two or more cells, one cell being insuffi¬ 
cient to overcome the resistance from polarization. 
The current was continued till the oxygen evolved 
at the positive pole ceased to combine with the lead, 
and was given off as gas. The cell was then discon¬ 
nected from the battery and discharged, by making 
connection between its electrodes, and a fresh charge 
given in reverse order, and continued as before until 



gas was given off. This process was continued for 
several months with intervening periods of repose, 
during which the cell remained charged; and the time 
of charging was increased from a few minutes on the 
first day, to several hours subsequently. In like man¬ 
ner the periods of repose were increased from hours to 
weeks and months. 

Chemical Reaction in the Plante Cell. — 
To understand the object of this treatment, it is neces¬ 
sary to examine the chemical reactions which take place 
in connection with the electric action. It will be 


































THE ELEMENTS OF ELECTRIC LIGHTIN'G. 


9 Q 9 
.2 ^ 

noticed that three distinct periods are required in this 
process : the period of charging, of repose and of dis¬ 
charging, during each of which a distinct chemical re¬ 
action occurs. During the charging, as already stated, 
peroxide of lead collects on the plate connected with the 
positive pole, and hydrogen on the one connected with 
the negative. But at first only a thin film of the per¬ 
oxide is formed, and a small amount of hydrogen col¬ 
lected, and the absorption of the gases soon ceases. 
The plates are then discharged, and during the discharge 
the peroxide, which is insoluble in sulphuric acid, is 
reduced to monoxide, PbO, which is immediately re¬ 
duced to sulphate of lead, PbS0 4 , by the acid present 
in the solution ; while the oxygen atom, taken from 
the peroxide, unites with the lead on the opposite plate, 
forming monoxide, which, in turn, is reduced to sul¬ 
phate. 

The result of the first discharge, then, is a thin film 
of the sulphate on each plate. The plates are then 
charged in reverse order, and the sulphate on the plate 
now connected with the positive pole is reduced by the 
oxygen to peroxide, while that on the opposite plate is 
reduced by the hydrogen to spongy lead, which adheres 
to the plate in a finely divided condition. As each 
subsequent charge, after discharge and reversal, pro¬ 
duces the same result, each coating continues to increase 
in thickness; and the spong}^ lead affording increased 
facility for the formation of the peroxide, the chemical 
reaction proceeds more rapidly. 

But the increased thickness of the peroxide soon in¬ 
terposes a strong resistance to this reaction, hence a 
period of repose previous to the discharge becomes ne¬ 
cessary ; and during this period local action, as it is 


THE STORAGE BATTERY. 


called, takes place. This consists in the reduction of 
the peroxide to sulphate from the reaction of the sup¬ 
porting lead plate ; the metallic lead having a strong 
affinity for oxygen, the peroxide parts with one atom 
of its oxygen, which unites with the lead, and the re¬ 
sulting monoxide is immediately reduced to sulphate by 
the acid. 

The chemical reaction of the discharge may now be 
more fully considered. Its result, as has been shown, is 
the formation of sulphate of lead on both plates ; and this 
sulphate, lying next to the plates, forms a resistance 
which impedes local action, which, as shown above, 
takes place during the period of repose. If the dis¬ 
charge is rapid, there occurs not only a reduction of 
peroxide to sulphate on the one plate, but also a reduc¬ 
tion of a portion of the sulphate on the other plate to 
peroxide through an excess of electrolytic oxygen ; and 
this reaction tends to reduce the difference of potential, 
and to produce electric equilibrium. 

But during the period of repose, this peroxide, being 
limited in quantity, and in close contact with the 
spongy lead, is rapidly reduced to sulphate; while the 
original peroxide coating on the other plate, from its 
greater thickness and the resistance of an excess of sul- 
pliate, is reduced much more slowly. Hence, there is a 
partial restoration of the original difference of potential, 
which accounts for the renewal of electric energy man¬ 
ifest in a partially discharged cell after a period of re¬ 
pose. These various chemical reactions result in an 
increased thickness of the peroxide deposit with each 
charge, while an increased thickness of spongy lead re¬ 
mains on the opposite plate after each reversal; and 
when the process has been continued long enough to 


234 THE ELEMENTS OF ELECTRIC LIGHTING. 

produce a sufficient thickness of each coating for a 
practically serviceable cell, the alternate charging and 
discharging with reversal is discontinued, and the cell, 
being ready for use, is always thereafter charged in the 
same direction. 

Each discharge, as shown, produces sulphate on both 
plates, but the oxygen generated on the plate connected 
with the positive pole reduces the greater part of the 
sulphate on that plate to peroxide; while the remaining 
portion, being in immediate contact with the plate, 
tends to preserve it from further disintegration. When 
the cell is put into practical use, these chemical re¬ 
actions continue, the same as during the forming pro¬ 
cess, sulphate being reduced to peroxide by each charge, 
and peroxide to sulphate by each discharge; and the 
electric energy varies as this reaction, and ceases when 
the chemical affinities are satisfied. 

The electric energy of the secondary cell, then, like 
that of the primary, is dependent on chemical reaction, 
the difference being that in the primary cell chemical 
reaction, with the generation of electricity, takes place 
spontaneously on the completion of the circuit, and con¬ 
tinues indefinitely, for months or years often in well- 
constructed cells; while in the secondary cell the elec¬ 
tric energy must first be supplied from an external 
source, and the action, both chemical and electrical, is 
limited and definite, dependent on the amount of elec¬ 
tric charge given. 

It does not appear that Plants himself fully under¬ 
stood the nature of the chemical reactions which take 
place, but proceeded on his practical observation of 
results; and it was not until 1882 that the chemical 
reactions producing these results were discovered by 


THE STORAGE BATTERY. 


the English electricians, Gladstone and Tribe, and 
described substantially as here given. 

A cell prepared in this way has a maximum E. M. F. 
of about 2.5-1 volts, and a variable resistance of half an 
ohm or less. When fully charged, it gives for several 
hours a current of varying constancy, dependent on 
the external resistance to be overcome, after which the 
current rapidly declines. 

The Plante Battery. — With a battery of these 
cells, Plante used a commutator by which they could 



Fig. 91. 


instantly be joined either in parallel or in series. Fig. 
91 represents such a battery, composed of twenty 
cells. 

The commutator is placed above, and is constructed 
with a cylinder of hard-rubber, which can be revolved by 
the milled head B. To this cylinder are attached, on 
opposite sides, two brass strips equal to it in length, 
against which press 40 brass springs, 20 to each strip, at¬ 
tached to opposite sides of a hard-rubber support, placed 
underneath the cylinder, as shown. These springs are 

















THE ELEMENTS OF ELECTRIC LIGHT INC. 


236 

connected by conductors with the buttery electrodes 
below; all the electrodes intended to be ol one kind 
being connected with the springs on one side, while 
those intended to be of the opposite kind are connected 
with the springs on the other side ; and thus the cells 
are joined in parallel. 

Between each opposite pair of springs, a brass pin 
passes through the center of the hard-rubber cylinder, at 
right angles to the strips; the ends projecting slightly, 
as shown in the figure. By a quarter revolution of the 
cylinder the contact of the springs is changed from 
the strips to the pins, and each opposite pair ot springs 
electrically connected, while insulated from all the 
others; and thus each positive electrode is connected 
through the springs and pin with the negative electrode 
of tlie adjoining cell; the connections with the springs 
being so arranged alternately as to produce this result, 
and thus join the cells in series. 

For charging, Plante joined the cells in parallel, 
and thus obtained a very low resistance, so that two 
Bunsen cells furnished a current of sufficient strength. 
But for discharging, he joined them in series, and ob¬ 
tained a maximum current equal to that ot thirty large 
Bunsen cells. But as the battery was not a generator, 
but an accumulator, it could only return the electricity 
which it had received less a certain percentage of loss 
from leakage, which Plante estimated at about ten per 
cent; and as it was used chiefly for such laboratory 
experiments as the heating of short wires, the external 
resistance being very low, the discharge was propor¬ 
tionally rapid, and lienee the strength ot the current 
quickly declined, the. maximum being maintained for 
only a few seconds. 


THE STORAGE BATTERY. 


237 


Such was the original battery of Plante ; an inven¬ 
tion ot the highest importance when regarded in the 
light of subsequent development, bearing the same 
relation, in this respect, to secondary batteries that 
Volta’s does to the primary, but of very limited prac¬ 
tical value, and, previous to 1880, scarcely more than a 
laboratory instrument. But it demonstrated several 
very important facts: 1. The practicability of con¬ 
structing a storage battery, which could give, for even 
a limited time, a continuous and very powerful current, 
fai in excess of that by which the charge was g’lven. 
2. That lead was especially well adapted for the elec¬ 
trodes, and water, acidulated with sulphuric acid, for 
the electrolyte. 3. That peroxide of lead was the best 
material for the positive plate, and spongy lead for the 
negative. Its principal defect was the tedious and 
expensive process of preparing the plates, a defect fatal 
to the practical use of the battery. 

Faure’s Secondary Cell. — About 1880, Camille 
A. Faure, another French electrician, constructed a cell 
similar to Plante's, in which he substituted plates pre¬ 
pared by a mechanical process for those prepared by 
the electric process. His method consisted in coating 
their surfaces with a paste of red lead (minium, Pb 3 0 4 ) 
and sulphuric acid, which, when subjected to electric 
action, was rapidly reduced to peroxide on the one 
plate, and spongy lead on the other. After this coat, 
ing was applied, it was covered with paper, and each 
plate then enveloped in felt, to retain the coating 
on the surface, and to insulate the plates from each 
other. They were then rolled together and placed in 
the acidulated water in the cell, and subjected to elec¬ 
tric action with reversal ; and in a few days the cell 
was ready for use. 


THE ELEMENTS OF ELECTRIC LIGHTING. 


238 

Chemical Reaction in the Faure Cell. — The 
chemical reaction in this cell, as described by Glad¬ 
stone and Tribe, is very similar to that in the Plante, 
but differs in the preliminary stage. The minium on 
the plate connected with the positive pole is reduced 
in part to peroxide by the absorption of two atoms of 
electrolytic oxygen, which, being added to the four 
oxygen atoms of the minium, make the oxygen atoms 
double those of the lead ; Pb 3 0 4 -f 0 2 = 3 Pb0 2 . But 
the sulphuric acid reduces part of the minium on this 
plate, as well as on the opposite plate, to sulphate; and 
this sulphate on the opposite plate is, in turn, reduced to 
spongy lead by the hydrogen, as in the Plantd cell. 
The reduction of minium to sulphate by the acid is as 
follows: Pb 3 0 4 + 2H 2 S0 4 = Pb0 2 + 2 PbS0 4 + 2 IP 2 0. 

The great advantage, then, of the Faure cell over the 
Plante, consists in the rapid reduction of minium 
instead of the slow reduction of metallic lead, thereby 
greatly reducing the cost. This cell, when subjected 
to practical tests, was found equal in energy to that of 
Plante’s, and it received the sanction of electricians of 
the highest standing, while its cheapness and facility 
of construction commended it at once to popular favor. 
The invention of the dynamo, too, having greatly 
reduced the expense and increased the facility of elec¬ 
tric generation, the great problem of the supply of 
electric energy, at economical rates, for general use as 
an illuminant and a motor, was apparently solved, since 
the electricity generated by the dynamo could be stored 
in the battery, to be transported and used wherever 
required for the propelling of cars or boats, the opera¬ 
tion of light machinery, and the illumination of dwell¬ 
ings and offices. 


THE STORAGE BATTERY. 



Faults of the Faure Cell. —But the new cell 
soon developed serious faults, which had to be overcome 
befoie these ends could be realized. The coating could 
not be made to adhere to the surface with proper uni¬ 
formity, but sloughed off partially, and collected in a 
mass at the bottom of the felt envelope. The space 
between the plates being entirely filled by the felt, 
the free circulation of the electrolyte necessary to the 
proper action of the cell was impossible ; and the felt, 
becoming corroded and partially removed in spots by 
the acid, soon ceased to act as an insulator; short-cir¬ 
cuiting ensued, and the cell became worthless. But 
the rapid preparation of the plates by mechanical 
process was a very important step in advance of the 
slow electric process of Plante ; and while the disap¬ 
pointment at the failure of the battery was as great as 
the enthusiasm with which its first appearance was 
hailed, electricians, confident of ultimate success, still 
worked patiently to overcome the faults which had 
been developed. 

The Improved Faure Secondary Cell. — The 
various improvements of Swan, Sellon, Volckmar, 
Shaw, and others, from 1880 to 1886, resulted in pro¬ 
ducing the improved cell shown in Fig. 92. It is made 
of different sizes, and with a variable number of plates, 


according to the purpose for which it is intended, the 
style here shown being the 23-plate stationary cell, having 
11 positive plates and 12 negatives,—those plates being 
known as positive which are connected with the positive 
pole in charging, and from which the external current 
flows in discharging, and the others being known as nega¬ 
tive. Each set is attached to a lead cross-bar above and 
at the center, by which the plates are held at a fixed dis- 


240 


THE ELEMENTS OF ELECTRIC LIGHTING. 


tance apart; the two sets interlocking, so that positive 
and negative plates alternate and are insulated from each 
other by two rows of hard-rubber forks. Each plate is J 
of an inch thick, and the space between adjacent, positive 
and negative plates, of an inch wide; and the two out. 
side, negative surfaces being inactive, each set has 22 in¬ 
terior, active surfaces. 

A thick plate of glass, under the central cross-bar and 
plate connections on each side, supports the plates, so 
as to leave a space underneath for the free circulation of 
the fluid; each set being supported, on its opposite side, 
by plate projections which rest on an insulating hard- 
rubber strip above each cross-bar as shown ; two stout 
rubber bands holding these supporting plates and the 
lower parts of the lead plates in position. A lead bar, 
projecting from the cross-bar of each set, can be bent 
into any convenient position for making connection with 
adjoining cells. 

These plates are immersed in water acidulated with 
36 per cent sulphuric acid, contained in a glass jar 10J 
inches long, 84 inches wide, and 9J- inches high ; the 
entire weight of jar and contents being 50 lbs. 

The glass jar has the advantage of allowing inspec¬ 
tion of the interior without disturbing the contents, by 
which the condition of the plates may be observed, and 
short-circuiting from the buckling of plates or the lodg¬ 
ing of loose paste plugs between them remedied; but 
its comparative frailty and weight are objections to its 
use for the portable cells required on cars and else¬ 
where. Hence a portable cell of the same capacity and 
number of plates is constructed with a covered, hard- 
rubber jar, made shorter below than above so as to 
furnish supporting ledges for the plates at the opposite 


THE STORAGE BATTERY. 


241 


ends, which take the place of the glass supporting plates 
employed in the stationary cell. The weight of this 
cell is 40 lbs., its height about the same as that of the 



Fig. 92. 

stationary cell, and its other dimensions about one 
fourth less. 

The 15-plate stationary cell has 7 positive plates, each & 
of an inch thick, and 8 negatives, each of an inch thick, 









































































































































































































































































































































































































































242 


THE ELEMENTS OF ELECTRIC LIGHTING. 


contained in a glass jar 10f inches long, 12J inches wide, 
and 13J inches high ; the entire weight being 130 lbs., and 
the storage capacity 300 ampere-hours, double that of the 
23-plate cell. The supporting plates are of hard-rubber, 
with openings for inspection, and are each held in position 
by two metal rods which pass through loops in the posi¬ 
tives at one end and in the negatives at the other, binding 
the plates of each set together below and furnishing electric 

connection between them. 
The plates are made of lead, 
cast in the form of grids, 
with square openings to hold 
the paste, as shown at A in 
Fig. 93, this form being the 
invention of Swan. Each 
opening is f of an inch 
square at the surfaces, but 
smaller at the center, the 
walls being thicker, sloping 
inward from each surface, as 
illustrated by the cross-sec- 
tion shown at i?,an improve¬ 
ment made by Sellon to pre¬ 
vent the paste from dropping out. These openings 
are filled with the paste of lead oxide and sulphuric 
acid ; minium. Pb 3 0 4 . being used for the positive plates, 
and litharge, PbO, for the negatives, each plug being 
held in its place by the peculiar form given to it by the 
opening. 

Electric Formation of the Plates. — In the 
electric formation of the plates at the factory, each set 
is charged separately, a set of temporary plates, or 
dummies, of each kind being used with each permanent 



R 








































THE STORAGE BATTERY. 


243 


set As the formation of the negatives requires a 
much longer time than that of the positives, litharge 
is preferred for them, being far more rapidly reduced 
than minium, which is used for the positives. But this 
difference of material compensates only partially for 
the difference in time : the negatives requiring six days 
for the reduction of the litharge to spongy lead, while 
the positives require only twenty-four hours for the re¬ 
duction of the minium to peroxide. But the use of 
the dummies prevents any inconvenience which might 
arise from this source, and renders the old process of 
reversal unnecessary. After the plates have been 


formed in this way, they are partially discharged before 
shipment, and require to be properly charged when the 
cells are completed and ready for use. 

Electro-Motive Force, Resistance, and Cur¬ 


rent of Cell. — The average E. M. F. of the cell is 
about 2 volts, its internal resistance from .001 to .005 
of an ohm, and its working capacity 300 ampere-hours. 
The current varies with the external resistance, and the 
rate of discharge can be regulated by this resistance. A 
medium rate gives the most satisfactory results, and is 
found to be the most economical. Hence, while a cur¬ 
rent of 300 amperes can be obtained and the cell dis¬ 
charged in an hour, such a rate is wasteful, and would 
soon injure the plates ; while with a 30-ampere current 
the cell will do efficient work for 10 hours, without 
waste or injurious results. 

It has been shown that the electric energy obtained 
by the discharge depends on the coincident chemical 
reactions, and that these reactions require time for 
their normal development; hence if the discharge is 
too rapid there will be abnormal chemical reaction with 


THE ELEMENTS OF ELECTRIC LIGHTING. 


244 

corresponding waste and injury. For the same reason, 
a medium rate of charging which allows sufficient time 
for the complete chemical reduction of the gases is the 
most economical; while with too rapid a rate, a portion 
of the gas escapes and is lost. The same result follows 
from overcharging, though in either case there is no 
injury to the plates, since there is no excess of chem¬ 
ical reaction as in discharging. As a result of 
the charging, a residual amount of gas adheres to the 
plates, oxygen on the positives, and hydrogen on the 
negatives, which does not enter into chemical combina- 
tion ; this increases the initial E. M. F. oi the discharge 
to 2.25 volts ; but as this gas is soon reduced, the E. M. 
F. falls rapidly, so that at the end of the first half hour 
it is about 2.04 volts* after which it remains nearly con¬ 
stant for several hours, gradually declining to two 
volts or less. When the cell is nearly discharged, the 
decline becomes very rapid, and if the discharge is con¬ 
tinued when this stage is reached, permanent injury to 
the plates is the result; hence the discharge should be 
stopped when the E. M. F. falls much below two volts. 

Cause of Buckling. — Buckling is a result of the 
formation of sulphate in discharging, producing un¬ 
equal expansion. If it were possible to obtain perfect 
uniformity in the material of the plates and in the solu¬ 
tion, so that the expansion in discharging, and the con¬ 
traction which follows in charging, should be uniform, 
buckling could not occur. But, like every other species 
of warping, it is a result of want of uniformity, either 
in the material, or in the action to which it is subjected, 
or in both. The acid, from gravitation, becomes denser 
in the lower part of the cell, and this affects both the 
chemical reaction and electric conductivity, both of 


Till.: STORAGE BATTERY. 


245 


which are greatest when the acid is most dense; and 
observation on buckled plates shows a curving from top 
to bottom, steadily increasing downward. But buck¬ 
ling does not interfere with the action of the cell until 
it has proceeded far enough to produce short-circuiting, 
by bringing plates into contact, or displacing plugs of 
paste. 

The pressure of the hard-rubber forks tends to 
prevent buckling and to maintain evenness of sur¬ 
face, keeping all the plates everywhere at equal dis¬ 
tances apart; while the rubber bands, by their elasticity, 
keep the pressure uniform, so that if buckling occurs, 
it is likely to affect all the plates equally, in which 
case short-circuiting cannot occur. The rubber bands 
and forks have also the very important qualities of 
being good insulators, and practically indestructible in 
the acid. 

Variable Resistance of Electrolyte. — The 
expansion of the plates while discharging is the result 
of the absorption of sulphuric acid to form the sulphate, 
and the acid absorbed in this way during the discharge 
is restored during the charging; from which it is evi¬ 
dent that the conductivity of the electrolyte is subject 
to continual variation ; steadily increasing during the 
charging until the full proportion of acid is restored, and 
declining during the discharge as the acid is absorbed; 
consequently the internal resistance of the cell varies 
inversely in the same ratio, and hence the necessity of 
the large percentage of acid used, that the resistance 
during the discharge may not become so great as to 
lessen the practical efficiency of the cell; as a smaller 
percentage would be liable to entire absorption before 
the termination of the discharge, leaving only water, 


240 


THE ELEMENTS OF ELECTRIC LIGHTING. 


which lias a very high resistance as compared with that 
of dilute acid. 

Too large a percentage of acid is also detrimental by 
producing an excess of sulphate, and consequent buckling 
of the plates during the discharge; so that the proper 
proportion to be used is of great practical importance, 
and the 36 per cent, already mentioned, seems to give 
the best practical results. 

The American Cell. —This cell is constructed with 
plates of pure rolled lead, each T \ of an inch thick, with 
grooves cut on both surfaces, as shown in Fig. 94, in 
perspective at A, and in cross section at B. Hard rub- 



A 



B 



94. 



her separators, made as shown at C, insulate the plates 
from each other when assembled in the cell. The active 
material is contained in the grooves, and formed from the 
plate itself by electrochemical action, as in the Plante 
cell, but by a much shorter process, the nature of which is a 
business secret, but which requires only two days for the 
complete formation of lead peroxide in the positives and 
spongy lead in the negatives. This material, being 



































































THE ST QUA GE BA TTER Y. 


247 


formed from the pure lead of the plate itself, is perfectly 
homogeneous throughout, and hence is claimed to he 
more durable and eliicieut than when formed from ap¬ 
plied lead oxides, liable to differences in quality, as in the 
Fan re plates. 

The plates are assembled in the cell,as shown in Fig. 

95, positives and negatives 
alternating, are bound to¬ 
gether vdtli stout rubber 
bands, and electrically con¬ 
nected by transverse lead 
bars soldered to clamps on 
the upper edges, and are 
immersed in a Hu id com¬ 
posed of one part sulphuric 
acid and live parts water. 

The cells complete, with¬ 
out fluid, range in weight 
from 4 pounds to 120, and 
in external size, from 34 
cubic inches to 2000. 



Fig. 95. 


The Chloride Accumulator. —The plates of this cell 
are about yq of an inch thick, and are constructed with 
small disks, which are fixed in a mold, and melted lead, 
alloyed with a small percentage of antimony, forced in 
around them under strong pneumatic pressure, producing 
a dense structure free from air holes, lhe disks for the 
positive plates are made of lead tape, grooved crosswise 
on one surface, and formed into flat rolls*, the grooves 
producing holes, or pores, through the disks which aie 
softened and rendered more porous by immersion foi 
a few T minutes in nitric acid. The edge is concave, so 
that the disk is larger at the surface than at the centei, 
and is therefore held in the plate like a rivet. 







































































248 


THE ELEMENTS OF ELECTRIC LIGHTING. 


The disks for the negative plates are made of a mix¬ 
ture of lead and zinc chlorides, fused together and cast 
in molds; and are convex at the edges, and hence 
smaller at the surface, than at the center, and therefore 
held in position by the inclosing surfaces of the plate. 

The negative plates are electrochemically formed by 
being placed, for two days, in a solution of zinc chloride, 
in contact alternately with zinc plates. The combination 
acting as a primary battery, removes the chlorides from 
the disks, leaving in them only highly porous, pure lead. 

The plates of both kinds are then assembled in a tank 
containing dilute sulphuric acid, each kind being con¬ 
nected together outside the tank by a conductor, alter¬ 
nating with the other kind in position, and insulated 
from them; and are subjected for some days to the action 
of a dynamo current, flowing constantly from the posi¬ 
tive to the negative set, by which lead peroxide is formed 
from the lead tape composing the disks of the positive 
plates, the spongy lead composing the disks of the nega¬ 
tive plates remaining unchanged. 

They are then placed in the cells, the positives being 
insulated from the negatives, which alternate with them, 
by separators of hard rubber which have circular con¬ 
tact knobs on both surfaces and inclose each positive 
plate at two points; and dilute sulphuric acid being 
added, the cells are ready for use. 

Durability of Storage Cells.— Manufacturers usu¬ 
ally guarantee for the positive plates a durability of one 
year, in constant practical use, with a normal current. 
The negatives are far from durable, not being subject to 
oxidation; and unless injured by buckling, last for an 
indefinitely long period. 



CHAPTER X. 


Electric Distribution. 

We have seen, in the preceding chapters, how elec¬ 
tricity may be generated, measured, accumulated, and 
made to produce light. It now remains to be shown 
how it may be distributed from the generator to the 
lamps. 

In small installations — as in the lighting of a single 
store, factory, or office building — distribution is com¬ 
paratively easy: but, with increase of area and of the 
number of lamps, the difficulties increase; so that dis¬ 
tribution over a large area in a town or city, from a 
central station, by means of conductors placed on poles 
or in underground conduits, supplying current to nu¬ 
merous consumers under varying conditions, accurately 
measuring the amount of current consumed by each, 
guarding against wastage of current, and against dan¬ 
ger to life and property from its effects, is a problem 
in electrical engineering of the greatest intricacy and 
magnitude. 

Arc-Light Distribution. — The methods of distri¬ 
bution for the arc light and the incandescent light are 
essentially different. As each arc lamp consumes a 
large amount of current, while the amount consumed 
by each incandescent lamp is comparatively small, the 
number of lamps fed by a given supply of current must 
vary in like proportion, and the means of distribution 


250 


THE ELEMENTS OF ELECTRIC LIGHTING. 


must be such as to furnish the proper amount to each 
without wastage. A ten-ampere current required by 
an arc lamp, for example, would supply twenty incandes¬ 
cent lamps of J an ampere each. Hence, it is found 
most practical and economical to adopt the series sys¬ 
tem of distribution in arc lighting, and the parallel in 
incandescent lighting. But arc lamps, especially for 
indoor Inditing, are often installed with incandescent 

o O' 

lamps on a parallel circuit; and as the E. M. F. required 
by them is much less than that required by the incandes¬ 
cent lamps, while the volume of current is much greater, 
the E. M. F. is reduced by passing the current through 
a resistance coil, at each arc lamp, and the volume of 
current increased by the comparative low resistance of the 
arc lamp. Incandescent lamps of large candle-power 
may be installed with arc lamps on a series circuit, but 
the difference between the two kinds, in E. M. F. and 
current volume, makes such installation undesirable. 

In both systems the E. M. E. or voltage ot the 
dynamo, and the resistance of the circuit, are the fac¬ 
tors which govern the supply of current, and the chief 
fundamental principles on which every installation is 
based, copper being always used for the conductors. 

Sektes Installation. — Fig. 96 gives a good general 
idea of an arc light installation ; X, X, X, representing 
the lamps in series, and I) the dynamo, series wound, 
with its -{- and — poles, as marked, from whicn the 
direction of the current can be ascertained. The posi¬ 
tion of the wires is a mere matter of convenience. 
They may be led through a building in any direction, — 
through or along walls, ceilings, or floors, — provided 
that proper insulation is maintained, and proper pre¬ 
caution against dangerous proximity to inflammable 


ELECTRIC DISTRIBUTION. 


251 


0 L 


LQ 




_ n 





substances or to the occupants. In such an installation 
the full current, leaving the dynamo at -f- and return¬ 
ing to it at —, passes through every lamp in the series. 
This current is maintained at a certain constant strength 
required by the construction of each particular style of 
lamp, and determined by the E. M. F. of the dynamo, 
and the full resistance of the entire circuit, including 
the dynamo, the lamps, 
and the conducting ' 

wires. The strength 
of current required 
varies greatly, ranging 
from ten to twenty 
amperes for series in¬ 
stallations in the vari- ($l 
ous leading arc light 
systems. Assuming a 
15-ampere current to 
be required by the 
ten lamps shown in 
Fig. 96, and that each 
lamp has a resistance 
of 3 ohms, the dynamo 
a resistance of 5 ohms, 

and a mile of No. 6 B. & S. wire, required for the circuit, 
a resistance of 2 ohms, then (10 X 3) -f- 5 -f- 2 = 37 
ohms the entire resistance, and 37 R X 15 C = 555 E. 
Hence, such an installation would require a 555-volt 
dynamo, each of the ten lamps requiring 55.5 volts. 

Hefner von A lteneck’s Regulator. —Each lamp 
in such a circuit is provided with a shunt similar to that 
used with the Brush lamp, as described on pages ISO- 
183, by which constancy ol current is maintained under 


QL 


D 


Fig. 9G. 
















252 the elements of electric lighting. 

change of resistance. This construction, which varies 
in different systems, was first introduced by Hefner von 
Alteneck, as mentioned on page 177, and will be readily 
understood from Fig. 97. The line L divides at i; the 
upper branch, composed of fine wire, being the shunt, 
and including the fine wire coil i£, reunites with the 
main line L x at the lower carbon holder b , thus passing 
round the lamp; the lower branch, composed of coarse 
wire, and including the coarse wire coil R v is connected 
with the lever c c v near its fulcrum d , the arm c x con¬ 



necting with the carbon holder «, and c with the iron 
rod s $, the weight of the rod counterbalancing that of 
the carbon and holder. This branch is thus connected 
directly with the lamp, reuniting with the main line at 
b. When the carbons &, k v are in contact, and a current 
passes, it divides at i in proportion to the respective 
resistance of each branch; the stronger current going 
through the coil 7£, and carbons k , k v to the line L x ; 
rod s s is drawn down by the greater attraction pro¬ 
duced by the stronger current through the low resist¬ 
ance coil R v the upper carbon K is lifted, and the arc 
lighted. 











ELECTRIC DISTRIBUTION. 


253 


The lighting of the arc increases the resistance of the 
lower branch, and in like proportion the potential differ¬ 
ence, or E. M. F., between L and L x ; and the strength 
of the current in R being increased by this increase of 
E. M. F. in the same ratio as that of R x is diminished 
by the increased resistance, the descent of the rod s s is 
checked by the opposing attraction of the coil R. The 
arc is thus maintained at its normal length by the oppos¬ 
ing attractions of the two coils ; any tendency to varia¬ 
tion of length in the arc tending to produce correspond¬ 
ing variation of the relative current strength in the 
opposing coils. 

It is evident that by varying the amount of wire in 
either coil, or changing its position with reference to 
the depth to which the rod s $ penetrates, any required 
adjustment of relative strength in attracting the rod may 
be obtained. 

The term differential is used to designate lamps con¬ 
structed in this manner. Without some such construc¬ 
tion, it would evidently be impractical to place lamps in 
series, as any variation of current strength in one lamp 
would affect every lamp in the series, producing continual 
fluctuation of the light, which would increase with the 
number of lamps; and if one lamp were extinguished, 
the interruption of the current would extinguish all the 
others; while the extinguishing of a differential lamp 
diverts the entire current through an automatic cut-out, 
similar to that of the Brush lamp, already described, by 
which an extinguished lamp is entirely eliminated from 
the circuit, and the full current permitted to flow to 
the other lamps; the constancy of the current at a 
given strength being maintained by the various device^ 
already described in connection with dynamos. 


254 


THE ELEMENTS OF ELECTRIC LIGHTING. 


This ideal representation of an arc-light installation 
is intended to embrace the leading principles which 
govern every such installation, while in their practical 
application they are modified according to the require¬ 
ments of each particular system. The number of lamps 
in one circuit fed by a single dynamo varies from one 
to fifty, or more; and the resistance, electro-motive 
force, current, candle-power, and methods of regulation, 
are numerous, and differ widely in the various systems. 

The dynamo is almost exclusively the direct current, 
series wound machine, the alternate current dynamo 
being seldom used now for arc lighting. 

In distribution to an extended area from a central 
station, in both arc and incandescent lighting, large 
conductors are used for the main leads, composed often 
of copper wires twisted together as a cable, to give 
the required flexibility combined with size. In large 
cities the mains, properly insulated, are usually required 
to be placed in underground conduits of lead or iron 
pipe, the iron being usually laid in the earth under the 
pavement, while the lead are inclosed in sub-ways, pref¬ 
erably of a composite insulating material, into which 
they can be drawn without disturbing the pavement. 
Branch circuits from the main line, and connected with 
it in series, extend into stores, office buildings, and 
factories; and the consumption of current is estimated 
by the number of hours light is required, and the size 
and number of lamps; a method which becomes the 
more practical since the lamps require daily attention 
by an expert, for renewal of carbons. 

Numerous independent main circuits extend from 
large central stations, fed by powerful dynamos; the 
number of dynamos running simultaneously varying 


ELECTRIC DISTRIBUTION. 


-O 

-o- 

-o- 

-o 


o 


-o 


255 

according to the amount of light required at different 
periods during each twenty-four hours, thirty to forty 
being often in operation at the same time in one room. 

Incandescent Light Distribution. — Incandes¬ 
cent lighting, as already stated, requires the parallel 
system of distribution. 

The difference between this and the 
series system will be understood from Fig. 

O 

98. Between two main conductors ex¬ 
tending from the dynamo, are placed, in 
parallel, several short lines connecting 
with the lamps, the current being thus 
divided among the lamps in proportion 
to their number and resistance, while in 
the series system the entire current passes 
through every lamp. This method is com¬ 
mon to both the direct and alternating cur¬ 
rent systems, which in other respects are 
so radically different, especially in their 
methods of distribution, that it is impor¬ 
tant to consider each separately. 

The Direct Current System. — 

The dynamo in this system has usually 
an effective E. M. F. of about 100 volts, 
after allowing a small percentage for loss in dis¬ 
tribution ; it is either shunt wound or compound 
wound, so that the current which goes to the lamp 
circuit is either wholly or partially independent of that 
which passes through the field-magnet coils, and hence 
the resistance of this dynamo in the circuit is far less 
than that of the series wound machine, in which the 
entire current passes through those coils. 

As the main conductors are required to carry a very 


^_ tr 


Fig. 98. 


















256 


THE ELEMENTS OF ELECTRIC LIGHTING. 


large current, they are proportionally large; the cross- 
section varying in proportion to variation of length, 
and number of lamps to be supplied, in order to equal¬ 
ize the resistance, and maintain constancy of current; 
it may be less than half a square inch, or exceed twelve 
square inches. As a fair illustration of the required 
size, it may be stated that the cross-section of a cable 
required to carry a current sufficient to feed 5,000 16 
candle-power lamps, at a mean distance of 4,000 feet 
from the dynamo, would be about 12.57 square inches. 
But as the current divides at each short parallel line, 
the size of the main conductors is proportionately re¬ 
duced as they extend ; while these short lines on which 
the lamps are placed, require only single wires of about 
No. 14 or 16 gauge. 

The resistance of the leading mains is, of course, 
very low; and the fall of potential between the dy¬ 
namo and the lamps, due chiefly to this resistance, 
varies usually from 2 l / 2 to 10 per cent. To reduce 
this loss so as to raise the potential at the lamps to a 
certain given percentage, without change in the effi¬ 
ciency of the dynamo, the cross-section of the mains 
must be increased in proportion to the square of the 
increase required in percentage; and as this must evi¬ 
dently make a great difference in the amount of copper 
required, this percentage becomes a very important 
factor, requiring careful calculation in every installa¬ 
tion. 

The resistance of the lamp, on account of the fine¬ 
ness and length of the carbon filament, is far in 
excess of that of the arc lamp; and the filament when 
cold has nearly double the resistance of the heated 
filament through which a full current is passing; hence 


ELECTRIC DISTRIBUTION. 


257 


the cold resistance of the circuit, when the current is 
first turned on, is far in excess of the subsequent hot 
resistance. 

Parallel Installation. — From these data we can 
form an ideal estimate of an installation arranged as 
in Fig. 98. If we suppose all the short parallel lines 
removed except the upper one with its lamp, or, what 
is practically the same, all the lamps except the upper 
one extinguished, the arrangement would not differ 
materially from that of an arc-light circuit having a 
single lamp; the entire current passing through this 
lamp, and its strength being determined by the effective 
E. M. F. of the dynamo, assumed to be 100 volts, 
divided by the entire resistance, including as before that 
of the dynamo, the conductors, and the lamp. Estimat¬ 
ing the resistance of the dynamo and conductors at 1 
ohm, and the hot resistance of the 16 candle-power fila¬ 
ment at 199 ohms, we have an entire resistance of 200 
, , 100A 7 , 

ohms, and = 2 an ampere, the current strength. 

But if two lamps be lighted, we furnish two paths of 
equal resistance, instead of one, between the mains, 
and reduce the filament resistance in the same ratio; 

lli -f- —jv— — = 100J ohms. And since the frac- 

2 Z 

tion in this case is practically insignificant, it may be 

100 E 

neglected, and we have = 1 ampere, the entire 


current strength, which, being equally divided between 
the two lamps, gives each ^ an ampere as before. 

For any small number of lamps the resistance varies 
inversely and the entire current directly as the number 
lighted., and the current per lamp remains practically 






258 


THE ELEMENTS OF ELECTRIC LIGHTING. 


constant, as shown, being equally divided among the 
entire number lighted. But as the resistance of the 
dynamo and circuit remains constant while that of 

4 / 

the filaments varies, it is evident that in the lighting 
of any considerable number of lamps the fraction, neg¬ 
lected above, would make a sensible difference in the 
ratio of resistance to E. M. F. Suppose that 100 were 
lighted, then the entire filament resistance would be 

1QQ /? 

- = 1.997?, and, adding in the 1 ohm constant re- 

100 55 


sistance, we have 2.99 ohms as the entire resistance ; 


hence 


100 E 
2.99 R 


= 33 t 4 /q( 7, which, divided among the 100 


lamps, gives about J of an ampere per lamp, instead of £ 
an ampere, with only one or two lighted. 

There is also a certain amount of current wastage, 
making an entire current variation of 15# to 20#, which 
must be provided for in order to maintain constancy of 
current and illumination. This, in the direct current 
system, is done by the introduction of resistance coils 
into the circuit, by which the current can be varied by 
variation of the resistance, and in the alternating cur¬ 
rent system by a direct variation of current in the con¬ 
verter. Hence when the indicator at the station shows 
a variation of current below or above the normal, by the 
lighting or extinguishing of any considerable number of 
lamps, the attendant makes the necessary correction by 
moving a switch either in the resistance jcx or converter, 
according to the system of lighting emp.oyed. 

The necessity for the greatly increased size of the 
mains, as compared with those used for arc lighting, 
becomes apparent when we compare the requirements of 
a 200-ampere current with those of a 10-ampere current. 




ELECTRIC DISTRIBUTION. 


259 


Multiple Series Installation. — The parallel 
system of distribution, shown in its simplest form in 
Fig. 98, is variously modified for different purposes. 
While it is generally preferable to place each lamp on 
its own separate branch between the mains, so that it 
can be lighted or extinguished without interfering with 
the other lamps, it is sometimes desirable to combine 
the series with the parallel system, producing what is 
termed the multiple series method; that is, several 
series in parallel with each other. This method is 
illustrated in Fig. 99, which 
shows three series in par¬ 
allel. Such a method is 
sometimes convenient for 
lighting a large room, as a 
public hall, store, or church, 
where a large number of 
lamps are required at the 
same time. By the method 
shown in Fig. 99, several 
such rooms in a large build¬ 
ing or in different build¬ 
ings can be lighted by the 
same dynamo. 

Large dynamos can be 
advantageously emplojmd 
for such installations; for 
the E. M. F. of the dynamo 
must correspond to the re¬ 
quirements of the lamps, 
and as the entire E. M. F. 
or electric pressure goes 
to every branch of the circuit, it is divided among 












260 THE ELEMENTS OF ELECTRIC LIGHTING. 

the several lamps on each branch in proportion to 
the number in each series, and the required voltage 
of each lamp. If the dynamo in Fig. 99 were a 
500-volt machine, and 100-volt lamps were used, .five 
lamps would be required in each series as shown, or 
ten 50-volt lamps; or series of five 100-volt lamps, 
and ten 50-volt lamps could be placed in the same 
installation. 

To prevent the extinguishing of all the lamps in a 
series, which must result from the extinguishing of any 
single one, an automatic cut-out is required for each 

lamp, as in arc lighting; and, to 
maintain constancy of resistance, an 
artificial resistance, equivalent to 
that of the extinguished lamp, must 
be switched in as the lamp is cut out, 
or else another lamp of equal resist¬ 
ance automaticallv lighted. 

Series Multiple Installa¬ 
tion. — Instead of serial groups 
placed in parallel, as just shown, 
parallel groups may be placed in 
series, as shown in Fig. 100, consti¬ 
tuting what is known as the series 
multiple method. While in the 
multiple series method the entire 
E. M. F. goes to each group, and 
is divided among its lamps, as has 
been shown, the entire current in 
the series multiple method goes to 
each group, and is divided among its 
lamps, in proportion to their number. A 2J-ampere 
current in the mains would therefore furnish a current 










ELECTRIC DISTRIBUTION. 


201 

of ^ an ampere to eacli of the five lamps in each group 
in Fig. 100. 

Such an installation is practically on the same basis 
as an arc-light series, the groups of incandescent lamps 
taking the place of the single arc lamps, and the E. M. F. 
of the dynamo, and general resistance of the circuit 
varying according to the number and resistance of the 
groups, so as to keep the current constant, while spe¬ 
cific regulation is required in each group, the E. M. F., 
resistance and current being here dependent on the 
parallel arrangement, and required to be the same for 
each lamp; and since the extinguishing of one or more 
lamps in a group would disturb this equilibrium, ab¬ 
normally increasing the E. M. F. of the remaining 
lamps, a regulator is provided, as in the Brush system, 
by which extra lamps are automatically lighted to take 
the place of those extinguished, or the whole group cut 
out, as on an arc-light series, in case the whole, or a 
large proportion, of the lamps are extinguished, so that 
the current flowing to the other groups in the series 
shall not be interrupted or diminished. 

Combined Arc and Incandescent Installation. 
— Arc lamps are sometimes placed in series with the 
groups of incandescent lamps, in which case the current 
strength of each group and that of each arc lamp must 
be the same. If arc lamps requiring a ten-ampere cur¬ 
rent are used, each incandescent group must absorb 
this current; hence, it may consist of ten one-ampere 
lamps, twenty half-ampere lamps, or any other number 
which multiplied by the current per lamp gives ten 
amperes. 

Distributers are, however, sometimes employed in 
which so much of the current as may be required for a 


262 THE ELEMENTS OF ELECTRIC LIGHTING. 

group is shunted through it, and a resistance coil pro¬ 
vided for each lamp, so that when a lamp is extinguished 
a coil of equal resistance is automatically substituted 
for it, and constancy of resistance maintained. 

It is, however, extremely difficult, in such an instal¬ 
lation, to maintain proper equilibrium between the arc and 
incandescent lamps, so as to produce satisfactory results. 

Instead of groups of incandescent lamps in parallel, 
single incandescent lamps of large candle-power, requiring 
a current of corresponding strength, may be placed in series 
with arc lamps requiring a current of the same strength. 

The Edison Three-Wire System. — The large 
amount of copper necessary for the leading maink of 
an incandescent light installation to carry the current 
required for any considerable number of lamps distrib¬ 
uted over an extended area, and remote from the central 
station, has proved financially a serious obstacle to prog¬ 
ress in this method of electric lighting. Among the 
methods devised to reduce this amount of copper with¬ 
out impairing the efficiency of the system, the Edison 
three-wire system stands prominent. In order to under¬ 
stand its advantages, we must compare it with the two- 
wire system. Fig. 101, letter A, represents two dynamos, 
each having its two leading mains of the usual size, 
carrying a current to lamps in parallel, and extending 
in the same general direction, the efficient E. M. F. of 
each, at the lamps, being estimated at 110 volts, after 
allowing a fall of ten per cent in the mains and connec¬ 
tions. If now these dynamos be joined in series, as 
represented at B , we can suppress two of the mains, 
and join each two lamps in series also. We would 
have, then, at A a practical E. M. F. of 110 volts to 
each lamp, and at B , of 220 volts to each two lamps in 


ELECTRIC DISTRIBUTION. 


263 

series, 110 to each lamp as before ^ tlie same amount of 
light is therefore obtained with half the number of mains. 

It is found, however, that the amount of copper 
required for a conductor carrying a current must vary 
inversely as the square of the E. M. F. ; having there¬ 
fore halved the number of mains, the current carried 
by the reduced number has double the E. M. F., and 



—o- 

—o— 

—o- 

—o— 

—c>- 

—o— 

r\ 

r\ 


u 

—a- 

-o— 



J£ 




B 


Fig. 101. 


+ 14- I 

c 


the resistance of each two lamps in series being four 
times that of each two in parallel, only one-fourth the 
current is required in the mains ; the whole amount of 
copper must therefore be reduced to one-fourth the 
original amount; which gives each of the two mains 
half, the cross-section ot each of the four original mains, 
the length remaining the same. 



















































2C>4 THE ELEMENTS OF ELECTRIC LIGHTING. 


But as there are the disadvantages already mentioned 
in a series connection of incandescent lamps, and as 
the number of lamps required, or in use simultaneously, 
is liable to vary on opposite sides of an installation, a 
third wire is inserted, as shown at C. Each lamp has 
now the same advantages of independent connection 
with the dynamo, as in the two-wire system, shown at 
A. If an equal number of lamps are burning simul¬ 
taneously in each row, the current will flow through 
the parallel branches from one dynamo to the other, as 
at B , the central wire remaining neutral; but if the 
number is varied by the extinguishing of lamps or 
otherwise, the third wire furnishes a path for the sur¬ 
plus current required by the row having the greater 
number lighted, which will flow to that side in conse¬ 
quence of the reduced resistance resulting from the 
greater number of branches open through the lighted 
lamps. 

We have now three mains at C each half the size 
of each of the four mains at A ; the whole amount of 
copper required at C is therefore only three-eighths 
of that required at A to accomplish the same result. It 
is found, however, that the third, or neutral wire, as 
it is termed, can be of reduced diameter, by which 
in practice a further reduction of about 4 1 / 2 per cent in 
the total amount of copper is effected. 

The feeding mains, on which no lamps are placed, 
extend as directly as possible from the central station 
to a central point in each lamp district, and are there 
connected with the lamp mains, whose size for different 
sections is made proportional to the number of lamps ; 
and these are tapped, as in other systems, at the various 
points where lamps are required, and connected with 


ELECTRIC DISTRIBUTION. 


20 5 

mains which extend into the buildings ; all the mains 
being constructed on the three-wire system. 

For underground conduits, iron pipes are used in 
this system, prepared in sections of convenient length, 
inclosing the three wires imbedded in a compact insu¬ 
lating compound of asphalt and petroleum, pumped in 
while hot; the wires being separated from the pipe and 
from each other by rope wound with space between the 
turns for the passage of the liquid, which solidifies at 
830° F.; solid copper rods being preferred to cables. 

The Storage Battery System. — The storage 
battery has recently become an important auxiliary in 
electric lighting in connection with the incandescent 
direct current system. 

Every installation must be equipped for its maximum 
requirement of light, which varies greatly at different 
hours and at different seasons; the supply required 
from 6 to 11 P.M. being far in excess of that required 
during any other part of the twenty-four hours, and 
that required for the long nights of the cold season 
exceeding that for the short nights of the warm season. 

To meet this maximum demand with a full supply 
of generators and power, requires a large investment of 
capital, especially for large central stations in cities, a 
considerable part of which is unemployed three-fourths 
of the time, entailing heavy expense for interest which 
must be added to the cost of the light furnished. This 
investment of unemployed capital can be reduced to 
the minimum by the use of storage batteries, as the 
supply of generators and power can then be made pro¬ 
portional to the average daily amount of light required 
during; the cold season instead of the maximum amount, 
and the generators run to their lull capacity both day 


THE ELEMENTS OF ELECTRIC LIGHTING. 


260 


and night; the surplus electricity, generated during 
the daily minimum requirement of light, being stored 
in the batteries to meet the daily maximum require¬ 
ment. 

The electricity furnished by the battery has a very 
important advantage for lighting over that furnished 
direct from the dynamo, the supply being absolutely 
steady, while that from the dynamo is subject to the 
fluctuations incident to the slipping of the belt, irregu¬ 
larity in the running of the engine, and sparking at the 
brushes, causing a certain amount of flicker in the light, 
which, even with the best regulation, can not be entirely 
eliminated. 

For lighting railroad cars the storage battery has 
proved very successful; a charged battery placed on 
the train furnishes the light required for a run of a 
thousand miles, while batteries at the terminal or way 
stations are meantime being charged, to be exchanged, 
on the arrival of the train, for those discharged, which 
in their turn are recharged for the next train. 

It is also successfully employed for such special 
lighting as is often required at theaters, art exhibitions, 
or private entertainments; and, to a limited extent, for 
lighting private residences, though too costly to come 
into general use for this purpose. 

The Induced Alternating Current System.— 
Since the amount of copper required to carry an elec¬ 
tric current varies inversely as the square of the 
E. M. F., if a 1,000 or a 1,200 volt dynamo could be 
substituted for one of 100 or 110 volts, the E. M. F. 
being multiplied by ten, the amount of copper required 
for the mains would be inversely, as the square of 
ten, equal to one hundred ; mains, therefore, of one 


ELECTRIC DISTRIBUTION. 207 

hundredth part the weight, could he employed. In 
the direct current system, however, with single lamps 
arranged in parallel, this would be impractical, 100 to 
1 ! 0 volt dynamos being the usual size practically 
admissible. But in the alternating current, induction 
system, dynamos of even greater E. M. F. can be suc¬ 
cessfully employed, though 1,000 volts represents the 
usual standard size. With such dynamos, and lamps 
at an average distance of a mile from the station, 
No. 1 B. & S. wire — about 3 / 10 inch diameter — is 
employed for the feeding mains. This is regarded as 
a practical, economical basis on which to maintain 
equilibrium between cost of power at the station and 
of copper in the mains; if, however, it is found desir¬ 
able to bring the current a distance of several miles, 
from some point where power is cheap and abundant, as 
in the case of water-power, so that economy of copper 
is more of an object than economy of power, dynamos 
of greater E. M. F. can be employed, and mains of 
reduced size; No. 5 B. & S. wire — 3 / 16 inch diameter 
— being often employed for such installations. 

This system, therefore, gives, for city lighting, the 
advantage of a cheap location in the suburbs for the 
dynamo and power station, from which distribution can 
be economically made to where property is more expen¬ 
sive, or for conveying the current cheaply from some 
point where water power is available ; also for cheap dis¬ 
tribution in sparsely settled districts. The converters, 
described in Chapter III., pages 55-60, are placed at the 
various points where lamps are required, and the small, 
primary, high potential current is, by this means, con¬ 
verted into a large, induced, low potential current pro¬ 
portioned to the number of lamps required at each 


THE ELEMENTS OF ELECTRIC LIGHTING. 


2(>S 

point; the alternating current rendering such trans¬ 
formation possible, which would not be possible with 
the direct current. 

The English electricians, Gaulard and Gibbs, first 
brought this system to public notice in 1883. They 
adopted the series method of distribution shown in big. 
102, the converters being placed in series on the pri¬ 
mary, high potential mains, and the lamps grouped in 
parallel on the secondary, induced current mains con¬ 



nected with each converter, as shown, but insulated from 
the primary mains. While constancy of current at the 
several groups could easily be maintained in this sys¬ 
tem by dynamo regulation, as on arc-light circuits, 
it was found exceedingly difficult to maintain the 
specific regulation required for constancy of potential 
at the lamps, as already explained in similar serial 
grouping in the direct current system ; the difficulty 
here being increased and complicated by the converters. 
Hence, this method, after many efforts to improve it, 













































EL E C TRIC I)IS Til I BUT ION. 


269 


was abandoned, and the parallel method, both for the 
primary and secondary mains, adopted. 

In this method, illustrated by Fig. 103, each con¬ 
verter being connected with the primary circuit in 
parallel, each group of lamps connected with it on 
the secondary circuit has the same independence of the 
other groups, as each single lamp in the multiple arc 
installation shown in Fig. 98 ; each lamp in like man¬ 
ner being connected in parallel with each secondary 
circuit as shown. 



Fig. 104 shows an air line installation with its con¬ 
nections in full. The primary mains X 1 , X 2 , extending 
from the station, are supported on insulators on the 
upper cross-arms of the poles P 1 , P 2 , P 3 , while the sec¬ 
ondary mains are similarly supported on the lower cross- 
arms ; the converters C\ C 2 , X 3 , being placed between 
the cross-arms, and their primary coils connected above 
to the primary mains, while their secondary coils are 
connected below to the secondary mains by short wires 
as indicated. Branch circuits, l\ / 2 , extend from the 
secondary mains into the buildings to supply the lamps 
d\ d 2 . The converters, as mentioned, vary in size, and 
are estimated by the number of lamps for which each 
is constructed to supply current; 10 to 80 lamps being 
the extremes, while the three ordinary sizes most in 













TIIE ELEMENTS OF ELECTRIC LIGHTING. 


2Tu 

demand are respectively for 20, 30, and 40, 50-volt, 16 
candle-power lamps. 

The very best construction and best insulation are 
exceedingly important in converters, the success of the 
system depending largely on their quality; since in 
dealing with currents of such high E. M. F. the failure 
of insulation may result in the burning out of the con¬ 
verter and its immediate connections. 



In estimating the comparative economy of the alter¬ 
nating and direct current systems, the cost of converters 
must be added to the alternating current estimate : while 
on the other hand, the amount of copper required in the 
alternating current mains being much less than in the 
direct current mains, and the construction of the dy¬ 
namo and auxiliary apparatus required at the station 
being simpler and less expensive, the reduction of 
expense in these items must be placed as an offset to 
the expense of converters. 

The parallel system of distribution, which has proved 




































ELECTRIC DISTRIBUTION. 


271 


to be the practical solution of the problem of distribu¬ 
tion by the induced alternating current, was originally 
suggested by Rankin Kennedy of Glasgow, and, it is 
claimed, was put in practical operation for the first 

time by William Stanley at Great Barrington, Mass, 
in 1885. 

The success of this experiment led to the develop¬ 
ment of the system on a large scale in 1887 by the 
Westinghouse Electric Company of Pittsburg, Penn., 
with which Mr. Stanley has been prominently con¬ 
nected, and to whose skill in the construction and 
perfection ol apparatus the success achieved is largely 
due. & 

M. M. Slattery of Fort Wayne, Ind., who also 
claims priority for the first practical experiment, should 
be recognized as one of the successful pioneers of this 
system; the promotion of the Slattery induction sys¬ 
tem, which is substantially the same as that here de¬ 
scribed, being immediately subsequent to that of the 
Westinghouse system. In England, Kapp and Mac¬ 
kenzie have been its most active promoters. 

The Primary Alternating Current System.— 
Incandescent lighting by the primary alternating current 
has already been referred to in connection with the 
Gordon dynamo in Chapter III., pages 46-49; 5,000 
twenty candle-power lamps, in multiple series, being 
illuminated by currents from a single dynamo, taken 
directly from the coils of its stationary armature; the 
Swan, 30-ohm lamp, being used. The Gordon system, 
in use for some time in England, has never been intro¬ 
duced into the United States; and Gordon himself has 
recently abandoned it for the direct current system. 

Within the last five years Charles Heisler of St. 


272 


THE ELEMENTS OF ELECTRIC LIGHTING. 


Louis, Mo., has introduced a system based on the primary 
alternating current method, with series distribution, 
low resistance, incandescent lamps ot BO candle-power, 
and a three to four ampere current carried by a No. 8 
copper wire. The obvious electrical difficulties involved 
in such a system Mr. Heisler claims to have successfully 
overcome; series distribution under these conditions 
being rendered practical by his short-circuiting device 
which cuts out the lamp in case a filament breaks, 
while the low resistance of the lamp filament adapts it 
to a current of much greater strength than that of the 
ordinary incandescent lamp, though less than half that 
of the ordinary arc lamp current; while the large 
candle-power specially adapts this lamp to the lighting 
of streets and large buildings. It is claimed that per¬ 
fect automatic regulation of E. M. F., current and re¬ 
sistance has been attained for every variation of load, 
from the full capacity of the circuit to that of a single 
lamp; dispensing not only with the converters required 
in the induction system, but also with the distributers, 
resistance boxes, and various safety devices required in 
other systems. Its principal feature, however, is the 
great economy of copper by the use of mains adapted 
to a 4-ampere current as compared with those required 
for a 200-ampere current. 

The Bernstein lamp is preferred both in this and in 
the induction system on account of its large filament 
of low resistance. 

Meters. — In all the various systems of incandescent 
lighting by parallel distribution, meters, such as have 
been described in Chapter VI., pages 150-155, for deter¬ 
mining the amount of current consumed, are connected 
with the mains at the various points where lamps are 


ELECTRIC DISTRIBUTION. 


L i o 


required, each company adopting some special style, 
and charging its customers in accordance with this 
measurement. 

Fuses. — As electric light wires are liable from 
accidental causes to become overheated and ignite in¬ 
flammable matter in close proximity, short fuses of soft 
metal are placed both in the mains and branch circuits, 
and wherever groups of lamps, as for chandeliers, or 
electrolliers, are required. If from any abnormal in¬ 
crease of current the temperature of the conductors 
approaches an unsafe degree, the fuse melts and opens the 
circuit; the fuses in the main and branch circuits being 
adjusted to the requirements of each circuit by differ¬ 
ence of size, which produces the difference of resistance 
necessary for the melting temperature ; a small fuse 
being more easily melted by a current of given strength 
than a large one. These fuses are attached by binding 
screws, and are easily replaced by new ones when melted. 

Switch-Boards. — Every station, whether for arc 
or incandescent lighting, is provided with a switch¬ 
board, embracing the terminals of the various circuits 
properly designated, so that connection between the 
dynamos and the circuits in a large building, or lamp 
district, can be instantly opened or closed, and the 
supply of current thus diminished or increased, accoid- 
ing to the number of lamps required at different hours. 

Several circuits may extend from the same dynamo, 
from different dynamos, or from connected dynamos, 
to the various rooms or floors of a large building, 01 the 
various sections of an extended area in a city ; all undei 
control of the operator at the station; so that any par¬ 
ticular room, floor, or section, can be eithci connected 
or cut off by moving a switch. 


274 


THE ELEMENTS OF ELECTRIC LIGHTING. 


Lighting Mines. — The incandescent system has a 
very important application in the lighting of mines ; the 
station being located at the mouth of the shaft, and 
current distributed through the various subterranean 
passages. This system is especially adapted to coal 
mines as a protection against the fatal accidents so often 
resulting from the ignition of inflammable gases ; the 
inclosure of the glowing filament in an air-tight glass 
bulb affording almost absolute security, since even the 
accidental breaking of the bulb would shatter and 
extinguish the filament before the gas could enter. The 
vitiating of the air by the consumption of oxygen, and 
the odor of burning oil from numerous lamps, is 
another evil which is eliminated. These advantages, 
and the superior illumination afforded, have made the 
incandescent lamp exceedingly popular with miners, 
wherever it has been introduced. Portable lamps with 
battery attachment are also in use among miners. 

Installation Rules. — The following is a brief 
summary of the rules usually given for the regulation 
of an electric light installation. 1. The dynamo should 
have a dry location; should not be exposed to dust 
or flyings; should be kept clean and well oiled, and 
its internal insulation should be practically perfect. 
2. All conductors in the dynamo room should be prop¬ 
erly supported, insulated, numbered, and conveniently 
arranged for inspection. 3. The construction of switches 
or commutators for opening or closing circuits, should 
be such that when moved or left there shall be no 
liability to heating or the formation of an arc. 4. The 
gauge of the wire on every part of the circuit should be 
proportioned to the current, and all junctions between 
conductors of different size should be fitted with fuses. 


ELECTRIC DISTRIBUTION. 


275 


so that the temperature of a conductor at any point cannot 
exceed 150° F. 5. All joints should be soldered, or electri¬ 
cally welded, and made mechanically and electrically per¬ 
fect. G. Complete metallic circuits should be used, and all 
connection with gas or water pipes as conductors avoided. 

7. Bare wires, passing over buildings, should be at least 
seven feet from every part of the building; and those 
crossing thoroughfares should be high enough to allow 
free passage for all vehicles and fire apparatus. 8. Un¬ 
derground wires should be thoroughly insulated, easily 
accessible, and their position clearly indicated. 9. The 
insulation of indoor wires should receive special care, 
so as to protect the building and its occupants against 
dangerous currents, and to prevent electric waste, 
particularly where the wires pass through walls or 
floors, or in close proximity to metallic masses ; and 
they should be incased in hard insulating material 
where the ordinary wrapping is liable to abrasion or the 
depredation of rats and mice; and, when placed beneath 
floors, they should be protected against mechanical 
injury and their position clearly indicated. Covered 
wire should have the preference for indoor work. Fre¬ 
quent electrical testing is exceedingly important, as the 
only safeguard against waste of current or injury to the 
conductors or insulation, since the ordinary indications 
of leakage by smell or otherwise, as in the case of gas ^ 
or water, are absent. 10. All bare outdoor wire should 
be thoroughly insulated at its supports, and incased in 
insulating material for at least two feet on each side. 
11. Arc lamps should be provided with globes as a pro¬ 
tection against flying sparks from the carbons; and all 
parts which require handling should be insulated from 

the circuit. 





INDEX 


A 

Accumulator, the chloride, 247, 248. 
Alternating current dynamos, 85-126. 
Alternating current system, the in¬ 
duced, 266-271. 

, the primary, 271, 272. 

Alternator, the, Stanley Two-Phase, 97- 
105. 

, Westinghouse Two-Phase, Constant 
Potential, 105-112. 

, Wood Single-Phase, Constant-Po¬ 
tential, 88-96. 

American Cell, the, 246, 247. 

Ammeter, the Weston, 151, 152. 
Ammeters, Ayrton & Perry’s spring 
voltmeters and, 156-159. 

, gravity, 159-161. 

, voltmeters and, 148. 

Ampere, the, 142. 

Arc-lamp, the, 176-203. 

, the inclosed, 203-205. 

, principles of the, 176-181. 

Arc-light carbons, 181-190. 

, automatic adjustment of, 194-196. 
Arc-light distribution, 249-255. 

Arc and incandescent installation, com¬ 
bined, 261, 262. 

Armature, the, 15-17. 

Armatures, closed circuit and open cir¬ 
cuit, 18. 

Armature’s mode of action, the, 29-34. 
Ayrton & Perry’s spring voltmeters and 
ammeters, 156-159. 

B 

Battery, the storage, 229-248. 

, the Plante, 235-237. 

, system, the storage, 265, 266. 
Bernstein carbons, the, 214-216. 

lamps, 215. 

Brushes, the, 18, 19. 

Brush dynamo, the, 48-55. 

arc-light lamp, the, 198-203. 

Bunsen photometer, the, 17'4, 175. 

C 

Candle, electric, the .Jablochkoff, 190, 

191. 

, the Jamin, 191-193. 


Carbons, arc-light, 181-190. 

, automatic adjustment of, 191-196. 
Carbons, incandescent light, 210-222. 

, the Edison, 210, 211. 

, the Lane-Pox, 211, 212. 

Carbons, the Cruto, 212, 213. 

, the Swan, 213, 214. 

, the Weston, 214. 

, the Bernstein, 214-216. 

Cardew voltmeter, the, 161-164. 
Chemical reaction in the Plante cell. 
231-235. 

in the Faure cell, 238. 

Chloride accumulator, the, 247, 248. 
Closed circuit and open circuit arina 
tures, 18. 

Coils, resistance, 172-174. 

Coulomb, the, 142, 143. 

Coulomb-meter, the Forbes, 160,107. 
Commutation, 25-29. 

Commutator, the, 17, 18.. 

Conductivity and insulation, 137, 133. 
Constant current dynamo, 37, 38. 

potential dynamo, 38. 

Construction, general details of iil.i 
ment, 216-222. 

of the incandescent lamp, 222 -227. 
Converter, the, 112-123, 269, 270. 

Cruto carbons, the, 212, 213. 

Current, 129-131. 

meter, the Edison, 104-100. 
system, the direct, 255-206. 

Current system, the induced alternat 
ing, 266-271. 

, the primary alternating, 271, 272. 
Currents, reversed, 23-25. 

D 

Difference of potential, 22, 23. 

Direct current system, the, 255-260. 
Distribution, electric, 249-275. 

, arc light, 249-255. 

, incandescent light, 255-274. 
Durability of storage cells, 248. 
Dynamo, the, 14-126. 

‘ , constant current, 37, 38. 

, constant potential, 38. 

, the, principles of, 14-39. 

Dynamo, the Brush, 48 55. 

‘ , the Excelsior, 40-48. 





278 


INDEX. 


Dynamo, the Siemens-Halske, type I. 
79 84. 

, the Thomson-Houston, 55-68. 

, the Wood, 69-72. 

Dynamo’s mode of action, the, 21-25. 
Dynamos, alternating current, 85-125. 
Dynamos, direct current, 40-84. 

, direct current and alternating cur¬ 
rent, 38, 39. 

, the General Electric Co’s multipolar, 
73-79. 

E 

Edison carbons, the, 210, 211. 
current meter, the, 164-166. 
lamp, the, 217. 

three-wire system, the, 262-265. 
Electro-motive force, 128. 

Electricity a mode of molecular mo¬ 
tion, 1-13. 

Electric candle, the Jablochkoff, 190, 
191. 

, the Jamin, 191-193. 

Electric distribution, 249-275. 
horse-power, the, 144. 
induction, 131-135. 
measurement, 145-175. 
potential, 127, 128. 
resistance, measurement of, 171- 
174. 

storage, 229, 230. 
terms and units, 127-144. 
units, 140, 141, 

Experiments in incandescent lighting, 
early, 207-210. 

F, 

Farad, the, 143. 

Faure’s secondary cell, 237, 

, chemical reaction in the, 238, 

, faults of the, 239. 

, the improved, 239-242. 

, electric formation of the plates 
for, 242, 243. 

, E. M. F., resistance and current 
of, 243, 244. 

, cause of buckling in, 244,245. 

, variable resistance of electrolyte 
in, 245, 246. 

Field-magnets, the, 19-21. 

Filament construction, general details, 
of, 216-222. 

Forbes coulomb-meter, the, 166,167, 
Force, electro-motive, 128, 
Foucault-Duboscq lamp, the, 196. 

Fuses, 273. 

G. 

Gaulard and Gibbs system, the, 268. 
Gravity ammeters, 159-161. 

n 

Hefner von Alteneck’s regulator, 251- 
255. 

Horse-power, the electric, 144. 


I 

Incandescent lamp, the, 200, 228. 

, construction of the, 222-227. 

Incandescent lighting,early experiments 
in, 207-210. 

Incandescent-light carbons, 210-222. 
distribution, 255-274. 

Inclosed arc lamp, the, 203 205. 

Indicator, the potential, 146-148. 

Induction, electric, 131-135. 

, magnetic, 135-137. 

, system, the Slattery, 271. 

Insulation, conductivity and, 137, 138. 

Intensity, quantity and, 138-140. 

Installation, series, 250, 251. 

, parallel, 257, 258, 

, multiple series, 259, 260. 

, series multiple, 260, 261. 

, combined arc and incandescent, 
261, 262. 
rules, 274, 275. 

J 

Jablochkoff electric candle, the, 190,191. 

Jamin electric candle, the, 191-193. 

Joule, the, 144. 

L 

Lamp, the arc, 176-203. 

, principles of the arc, 176-181. 

, the sun, 193, 194. 

, the Foucault-Duboscq, 196, 

, the Serrin-Lontin, 196-198. 

, the Brush, 198 203. 

Lamp, the incandescent, 206-228. 

, construction of, 222-227. 

, Reynier’s, 206, 207. 

, Starr's, 208. 

, the Bernstein, 215. 

, the Edison, 217. 

, the Weston. 218. 222-227. 

, the Swan, 224-226. 

, position of, 227. 

Lane-Fox carbons, the. 211, 212. 

Light unit, the standard, 174. 

Lighting mines, 274. 

, vacuum tube, 227, 228. 

M 

Magnets, the field, 19-21. 

Magnetic induction, 135-137. 

Measurement, electric, 145-175. 
of electric resistance, 171-174. 

Meters, 272, 273. 

Microfarad, the, 143. 

Milliammeter, the Weston, 152. 

Mines, lighting, 274. 

Mode of action, the armature’s, 29-34. 

, the dynamo’s, 21-25. 

Multiple series installation, 259, 260. 

Multipolar dynamos, the General Elec¬ 
tric Co.’s, 75-79. 

O 

Ohm, the, 141, 142. 


1 





INDEX. 


279 


p 

Parallel installation, 257, 258. 

PlanttPs secondary cell, 230, 231. 

Plant,*? cell, chemical reaction in the, 
231-235. 

Photometer, the Bunsen, 174, 175. 
Position of lamp, 227. 

Potential, difference of, 22, 23. 

, electric, 127, 128. 
indicator, the, 146-148. 

Q 

Quantity and intensity, 138-140. 

R 

Resistance, 128, 129. 
coils, 172-174. 

Regulator, Hefner von Alteneck’s, 251- 
255. 

Reversed currents, 23-25. 

Revnier’s lamp, 206, 207. 

Rules, installation, 274, 275. 

S 

Secondary cell, Faure’s, 237. 

, Faure, chemical reaction in the, 
238 

, Faure. faults of the, 239. 

, Faure, the improved, 239-242. 

, Faure’s electric formation of the 
plates for, 242, 243. 

, Faure’s. E. M. F., resistance and 
current of, 243, 244. 

, Faure’s, cause of buckling in, 244, 
245. 

, Faure’s, variable resistance of 
electrolyte in, 245, 246. 

, Plante’s, 230, 231. 

Series installation, 250, 251. 

multiple installation, 260, 261. 

Series, shunt, and compound winding, 
34 37. 

Serrin-Lontin lamp, the, 196 198. 
Siemens-Halske dynamo, the, Type I. 
79-84. 

Slattery induction system, the, 271. 
Stanley Two-Phase, Constant Potential 
Alternator, the, 97-105, 

Starr’s Lamp, 208. 


Storage battery, the, 229-248. 

system, the, 265, 266. 

Storage cells, durability of, 248. 

Spring voltmeters and ammeters, Ayr¬ 
ton & Perry’s, 156 159. 

Sun lamp, the, 193, 194. 

Swan carbons, the, 213, 214. 
Switch-boards, 273, 

System, the Gaulard and Gibbs, 268. 

T 

Terms and units, electric, 127-144. 
Thomson-Houston dynamo, the, 55-68. 
Thomson recording watt-meter, the, 
167-171. 

Three-wire system, the Edison, 262-265. 
Transformer, the, (See Converter) 56-60, 
259, 270. 

, the Westinghouse rotary, 123-125. 
U 

Units, electric, 140, 141. 

y 

Vacuum tube lighting, 227, 228. 

Volt, the, 141. 

Voltmeter, the Cardew, 161-164. 

, the Weston, 148-151. 

, the Wirt, 152-156, 

Voltmeters and ammeters, 148. 

, Ayrton & Perry’s spring, 156-159. 

W 

Watt, the, 143,144. 

Watt-meter, the Thomson recording, 
167-171. 

Westinghouse Two-Phase, Constant 
Potential Alternator, the, 105-112. 
rotary transformer, the, 123-125. 
Weston ammeter, the, 151, 152. 
carbons, the, 214. 
milliammeter, the, 152. 
voltmeter, the, 148-151. 

Winding, series, shunt, and compound, 
34-37. 

Wirt voltmeter, the, 152-156. 

Wood dynamo, the, 69-72. 

Single-Phase, Constant Potential 
Alternator, the, 88-96. 





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LORING, A. E. A Hand-book of the Electro-magnetic Telegraph. 16mo, 
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NO AD, H. THE. The Student’s Text-book of Electricity. A new edition, care¬ 
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